My DH who has hiked up Mt. Kilimanjaro as well as Everest basecamp and Aconcaqua suggests that you get there 3 or 4 days to acclimate first like many posters have suggested. There are many things to see there like the National Park, a trip to Ngorongoro etc before the climb. He says the key is to go slow. He does not recommend going up in 3 days which he did but he’s been a long distance runner since high school. There are 5 different routes up to Kilimanjaro and he said for you to research the different routes to suit your physical ability. He took the Umbewe route.
He also recommends Diamox.
I didn’t accompany him on those hikes but we did the trip to Machu Picchu together. I tried Diamox while at home to see if there’s any adverse side effects first and I took it again while arriving at Cusco. I did quite well on the trip, no altitude sickness at all.
“I’ve never been to Kilamanjaro but I’ve done a fair bit of high altitude hiking in the Sierra Nevada range. The best thing to do is to spend a few days acclimating to high altitude just before the hike. I stay at 9,000 feet for a day or two before going up to 10 or 12,000. Drink plenty of water.”
When my husband did a half marathon up to Pike’s Peak this summer, he went out 10 days early to acclimate, starting in Breckenridge (about 9500 feet), and hiking up a number of 14,000 footers. He felt pretty good the first few days, except for having a hard time sleeping. On the other hand, I felt really awful for about 3-4 days. It took me much longer to acclimate, and I’m not really sure why, perhaps people deal with it differently. I wonder if it made a difference that his level of fitness was significantly better than mine? I’m pretty bad about keeping hydrated, which could be a factor. But I also wonder if I took that Diamox, if it would have been easier, though maybe that would be wimpy for just 9500 feet.
What really irritated me about the high altitude was that I couldn’t even drink more than a glass of wine without feeling really hung over in the morning. I probably have my priorities all screwed up. However, our bar bill was very low that trip. 
I used to go backpacking in the Sierras in my 20s. Our friends who picked up the permissions would come a day early and spend a night at 8000, while we arrived and immediately had to get over a 12000 foot pass though we camped at about 10000. I always had a headache the first night. Even after the better part of a week, I never felt as strong as I do at sea level, though the hiking was so gorgeous it was worth it.
Are you going to have time to see the rest of Tanzania? It’s gorgeous. I spent three summers there, but never did any climbing.
People can react VERY differently- despite levels of fitness. Also, it can vary from time to time. I have a friend who has completed the Leadville 100 running race several times, but this past summer he was vacationing in Leadville and after several days of being OK, he got severe altitude sickness (the kind where you can die if you don’t get to a lower elevation ASAP). It’s nothing to mess with! I go to Crested Butte (over 9400) every summer and I generally do OK- maybe slight headaches for a day and running is tough, but the 14000 stuff really gets me.
Fewer than half the climbers who attempt Kilimanjaro make it. Look it up. You need to be very fit to attempt this. My SIL trained for it by climbing Rainier several times.
One of my younger coworkers did this about 10 years ago. She trained extensively (lots of hours on the stair trainer with weighted backpack ). Her trip was longer than those mentioned up thread. I think it was 9 or 10 days. Lots of “hike high, sleep low”. They kind of circumnavigated the peak before hitting the top.
If they are starting out at 5,000’, getting there early may not help that much to acclimatize unless you climb up the first stretch a few times on your own. Not sure how much sleeping at 5,000’ would help. In my case, I don’t notice altitude until about 8-9,000’.
Level of fitness does not predict high altitude issues.
I have had issues with this, traveling yearly from New Jersey to Summit County Colorado - mother - in- law lives at 9,000 ft
I follow this regimen of Advil the day before and have had it under control for Last several years !
http://healthland.time.com/2012/03/20/ibuprofen-can-prevent-altitude-sickness/
Agree that fitness level, and taking precautions does not preclude altitude sickness. They hold conferences in Denver and Keystone, CO at high altitudes of 5,200’ and 9,173’ respectively. Every year, they have some participants including MDs get altitude sickness. Allowing the body to gradually adjust to altitude helps, but even fit folks can end up with altitude sickness. Both H and S had it when we went to the Sierra Nevadas and they were fitter than D and I, who didn’t have altitude issues.
My sister lives in Denver but still gets altitude sickness when she goes to the mountains. Not always, bUT occasionally… She skis and clips 14ers, and even owns a house in Summit county, but still gets altitude sickness occasionally. My kids experience it when they come from lower altitudes.
For the reverse, my sister trained for a marathon in Colorado and breezed through it at a lower altitude.
Drink water. So much water. Way more than you think you need. Being fit will help for the hike but it doesn’t provide immunity from altitude sickness.
Definitely take a less expensive trip to high altitude first to see how you adjust.
@sorghum, I’m wondering if you have gone on this trip yet, and how it went? Very curious, in particular, because my husband is talking about us doing it.
@busdriver No, not yet, but I am still working on the related fitness program …
My neighbor’s brother died on this climb. He was a fit man in his late 40s. So it’s definitely not risk free, but I’m sure you know that!
Wow, @LBowie, that’s sad and sobering. I guess the good thing is that he was doing what he wanted when he died.
@LBowie, do you know the circumstances of the death? I am concerned about altitude sickness for a venture I would like to undertake. After I’ve heard from 2 younger acqaintances who had trouble with this in Colorado during the ski season I’m rethinking my plans.
Okay, keep us updated, sorghum.
That is awful, LBowie. What happened, do you know?
Momofadult, how high are you planning on going? Going to Colorado, I could see people having a big problem in Breckenridge (base about 9500, tops about 11K I think), if they flew right into Denver or somewhere near by and didn’t acclimate at all. I generally have little problem with altitude, and it definitely affected me when I did it. This year we will spend a night at Steamboat, three nights in Aspen, and then go to Breckenridge
I’m researching Nepal. There are many reasons why this trip wouldn’t happen - acquiring altitude sickness in this location one of the biggest concerns. It is so tempting though!
I am not really sure of the circumstances. I know two other people who climbed it and made it safely, a father and teenage son. The father, who is an experienced adventurer, said it was a lot harder than he expected when nearing the summit.
Regarding Nepal, my husband and son went with the aim of making it to the lowest Everest base camp. My son got altitude sickness and they didn’t make it as far as they planned. However, it was a memorable trip. One day I would like to trek to Namche Bazaar, if I can stomach flying into Lukla. That is a big if!!
I just looked up statistics for Kilimanjaro and found 1000 evacuations a year and 10 deaths a year, with suspected more that are unreported. Altitude sickness the culprit.
I also know someone who started up Kilimanjaro, but didn’t make it to the top. She could tell that continuing was not going to be a good idea, so disappointment, but no tragedy.
@LBowie, thanks for the Nepal report. My goals aren’t as lofty as any of the Everest camps, just Katmandu which is lower. Altitude sickness should be less of a concern there, but still not something I want to experience.