This review discusses the unmet needs of patients with attention deficit/hyperactivity disorder (ADHD) who are transitioning into adulthood. Although awareness and recognition of ADHD in children, adolescents, and adults have improved in recent years, there is often an interruption in management of the disorder when adolescent patients transition to adult health care services. This review has the following objectives: (1) to identify key issues patients with ADHD (with or without an early diagnosis) face during transition into adulthood; (2) to review the current clinical practice and country-specific approaches to the management of the transition into adulthood for patients with ADHD; (3) to discuss challenges facing clinicians and their patients when drug treatment for ADHD is initiated; (4) to review current ADHD guidelines on transition management in Hong Kong, Singapore, South Korea, Turkey, and Africa; and (5) to examine economic consequences associated with ADHD. The review suggests that the transition period to adult ADHD may be an underresearched and underserved area. The transition period plays an important role regarding how ADHD symptoms may be perceived and acted upon by adult psychiatrists. Further studies are needed to explore the characteristics of the transition period. If only a fraction of adolescents go on to have mental disorders during adulthood, especially ADHD, it is crucial to identify their characteristics to target appropriate interventions at the beginning of the course of illness. There continues to be low recognition of adult ADHD and a severe lack of medical services equipped to diagnose and care for patients with ADHD transitioning from child to adult services.