Objective: There is an updated conceptualization of whole-lifespan attention-deficit hyperactivity disorder (ADHD), promoted by awareness of probable persistence of impairment into adulthood. We investigated cognition trajectories from adolescence to mid-adulthood in ADHD. Method: Data of 240 patients with ADHD and 244 healthy controls (HCs) were obtained; clinical symptoms and neuropsychological functions were assessed using the various tests. Results: Compared to HCs, patients with ADHD except 35 to 44 age interval showed lower full scale intelligence quotient. They showed decreased verbal comprehensive scores except in the 35 to 44 age interval and working memory scores in all intervals. In the Comprehensive Attention Test, patients with ADHD showed increased working memory error frequencies except in the 15 to 17 age interval and divided attention omission error in all intervals. Conclusion: Adults with ADHD showed deficits not in simple attention but in complex attention, including divided attention and working memory.