Objective: Developmental and subtype differences in behavioral assets and problems were examined in 318 children newly diagnosed with ADHD. Method: Three age groups were compared: 4 to 6.9 years (n = 95), 7 to 9.9 years (n = 136), and 10 to 15 years (n = 87); with two subtypes examined: inattentive (n = 151), and hyperactive/combined (n = 167). Data on assets and problems were obtained from parental questionnaires. Analyses were conducted for the assets and problems data with subtype and age as between group factors. Results: Younger children had more problems with hyperactivity, and the eldest group had more externalizing problems. The hyperactive/combined subtype exhibited more problems than the inattentive subtype. Also the younger group had more assets than the eldest group. Conclusion: Children who possessed greater assets had fewer behavioral problems, with assessment of assets and problems important in the diagnosis of ADHD. (Contains 7 tables.)