Attention-Deficit/Hyperactivity Disorder (ADHD) is a developmental disorder which begins in childhood. It is now recognized that ADHD persists into adolescence and adulthood in the majority of cases. Significant psychiatric comorbidity, particularly substance abuse, antisocial personality disorder, and mood and anxiety disorders occurs in adolescent and adult ADHD. Perhaps one fifth of childhood cases of ADHD may also have co-morbid learning disorder. Significant legal, academic, social, and occupational problems have been observed in adults with ADHD. The clinician faces a diagnostic and treatment challenge in trying to determine whether ADHD and learning disabilities (LDs) are present in the adult patient. Treatment and recommendations for accommodations in institutions of higher education and the workplace may rest on accurate discrimination between ADHD and LD.