The first phase was a double-blind crossover design of methylphenidate in the treatment of adult ADHD. The second phase consisted of an open-label extension trial of methylphenidate in adult ADHD. It was hypothesized that methylphenidate would prove more effective than placebo in treating ADHD symptoms during the first phase. It was also hypothesized that methylphenidate responders from the double-blind trial would continue to benefit from treatment in the second phase. Improvement would include both ADHD symptoms and social adjustment.

All patients received a single-blind week on placebo, followed by a double-blind random assignment crossover trial of methylphenidate and placebo, with each double-blind phase lasting two weeks. Subjects who experienced moderate or marked improvement on methylphenidate would be allowed to enter a long-term, open-label trial. ADHD symptom severity was measured monthly by a structured interview, the Wender-Reimherr Adult Attention Deficit Disorder Scale (WRAADDS), Clinical Global Impression - Improvement (CGI-I) and Global Assessment of Functioning (GAF). Social functioning was assessed by the clinician administered version of the Weissman Social Adjustment Scale (WSAS). Dosing was determined by clinical judgement, symptom improvement and AEs.

Inclusion Criteria:

• Ages 21-55 years; male and female; met "Utah Criteria" for adult ADHD; 95th or higher percentile on the Parent Rating Scale and/or the Wender Utah Rating Scale;

Exclusion Criteria:

• Patients with other axis-I and axis-II diagnoses were excluded as were patients with significant medical problems.