Some people grow out of their childhood attention-deficit/hyperactivity disorder (ADHD) and some don't. In fact, around 50% of individuals diagnosed as children continue to suffer from ADHD as adults. Researchers are trying to understand the reasons why, and whether there are any differences that distinguish the two groups. Gender, ethnicity, socioeconomic class, and symptom severity have already been ruled out as potentials. So, perhaps there is a distinguishing variable in the brain?