To verify the hypothesis that there is different gender ratio of attention-deficit/hyperactivity disorder (ADHD) among adults compared to children and adolescents in the clinical setting among Asian population. The nationwide population-based database containing data on enrollees in the National Health Insurance program in Taiwan during 2000-2007 was used in this study, and we investigated the lifetime gender ratios of administrative prevalence and incidence in healthcare-seeking ADHD patients (n=228,029). The male-to-female ratios of diagnosed incidence and prevalence of child/adolescent ADHD (age < 20 years) ranged from 3.39 to 4.07 and 3.87-4.31, respectively. The male-to-female ratios of diagnosed incidence and prevalence of ADHD in the adult group (age 20-65 years) ranged from 0.24 to 0.76 and 0.35-0.98, respectively. In conclusion, there was substantially increased female-to-male ratio in adults ADHD compared to children and adolescents in the clinical setting. Further researches on the management and mechanism are needed. (C) 2016 Elsevier Ireland Ltd. All rights reserved.