You can be diagnosed with ADHD once you’re in the military, and through all of your training. My brother joined the National Guard about 15 years ago, he’d gone to Basic, but had a break between it and AIT (the school where you learn your job). My oldest daughter and I had just been diagnosed, and he got evaluated and diagnosed during that break. He was told that if he’d waited until after AIT to be diagnosed, he’d have been fine.Supposedly they’ve relaxed their policy on enlistment, but basically you can’t join if you are diagnosed and are either receiving treatment or actively have symptoms. https://www.thebalance.com/new-asthma-and-add-adhd-policy-3353970 So basically, if you’re diagnosed, you’re not getting in. However, it certainly seems like there are a lot of folks in the military with undiagnosed ADHD, but I could be wrong. It’d be interesting to do a study to try and find out what the percentage is. Maybe that would be enough to get the military to relax their rules.