Objective: This study examines adolescent-specific practical problems associated with current practice parameters for diagnosing attention-deficit/hyperactivity disorder (ADHD) to inform recommendations for the diagnosis of ADHD in adolescents. Specifically, issues surrounding the use of self- versus informant ratings, diagnostic threshold, and retrospective reporting of childhood symptoms were addressed. Method: Using data from the Pittsburgh ADHD Longitudinal Study (PALS), parent, teacher, and self-reports of symptoms and impairment were examined for 164 adolescents with a childhood diagnosis of ADHD (age M = 14.74 years) and 119 demographically similar non-ADHD controls (total N = 283). Results: Results indicated that 70% of the well-diagnosed childhood ADHD group continued to meet "Diagnostic and Statistical Manual of Mental Disorders" (4th ed., text rev.; American Psychiatric Association, 2000) diagnostic criteria for ADHD in adolescence; however, an additional 17% possessed clinically significant impairment in adolescence but did not qualify for a current ADHD diagnosis. The optimal source of information was combined reports from the parent and a core academic teacher. Adolescents with ADHD met criteria for very few symptoms of hyperactivity/impulsivity, suggesting a need to revisit the diagnostic threshold for these items. Additionally, emphasis on impairment, rather than symptom threshold, improved identification of adolescents with a gold-standard childhood diagnosis of ADHD and persistent ADHD symptoms. Parent retrospective reports of baseline functioning, but not adolescent self-reports, were significantly correlated with reports collected at baseline in childhood. Conclusions: Recommendations are offered for diagnosing ADHD in adolescence based on these findings. (Contains 6 tables and 3 figures.)