Objective: We performed a 10-year prospective follow-up of a childhood-ascertained (6-12 years), ethnically and socioeconomically diverse sample of girls with attention-deficit/hyperactivity disorder (ADHD; N = 140: combined type [ADHD-C] n = 93; inattentive type [ADHD-I] n = 47) plus a matched comparison group (N = 88). Girls were recruited from schools, mental health centers, pediatric practices, and via advertisements; extensive evaluations confirmed ADHD versus comparison status. Method: Ten-year outcomes (age range 17-24 years; retention rate = 95%) included symptoms (ADHD, externalizing, internalizing), substance use, eating pathology, self-perceptions, functional impairment (global, academic, service utilization), self-harm (suicide attempts, self-injury), and driving behavior. Results: Participants with childhood-diagnosed ADHD continued to display higher rates of ADHD and comorbid symptoms, showed more serious impairment (both global and specific), and had higher rates of suicide attempts and self-injury than the comparison sample, with effect sizes from medium to very large; yet the groups did not differ significantly in terms of eating pathology, substance use, or driving behavior. ADHD-C and ADHD-I types rarely differed significantly, except for suicide attempts and self-injury, which were highly concentrated in ADHD-C. Domains of externalizing behavior, global impairment, service utilization, and self-harm (self-injury and suicide attempts) survived stringent control of crucial childhood covariates (age, demographics, comorbidities, IQ). Conclusions: Girls with childhood ADHD maintain marked impairment by early adulthood, spreading from symptoms to risk for serious self-harm. Our future research addresses the viability of different diagnostic conceptions of adult ADHD and their linkages with core life impairments. (Contains 2 tables.)