Q: How common is adult A.D.H.D.? What are the symptoms and is it possible for someone who was not diagnosed with it as a child to be diagnosed as an adult?...The Attention Deficit Disorder Association, an organization founded in 1990 for adults with A.D.H.D, saw its membership nearly double between 2019 and 2021. In addition, Children and Adults With Attention-Deficit/Hyperactivity Disorder, or CHADD, reported that the highest proportion of people who call their A.D.H.D. help line are adults seeking guidance and resources for themselves.