We present a novel condition, designated as a primary disorder of vigilance, that has symptoms which overlap those of attention deficit-hyperactivity disorder. Vigilance is the state of being watchful, awake, and alert. When vigilance is lost, the individual has difficulty sustaining attention. The most obvious evidence of lowered vigilance is motor restlessness (fidgeting and moving about, yawning and stretching, talkativeness, or a combination of these) to improve alertness when sitting or standing still or when involved in tasks requiring continuous mental performance. When prevented from being active to stay awake, persons with lowered vigilance will stare off, daydream, show minor hyperactivity, and finally may fall asleep. They will also have decreasing attention to current activities and usually avoid or lose interest in structured or repetitive activities (complaining of boredom and monotony). The primary disorder of vigilance (for which criteria have been established) is a dominantly inherited condition with onset in early childhood and worsening symptoms with age. Persons with the primary disorder of vigilance have a remarkably kind and caring temperament. When untreated this disorder can cause chronic failure at school and work, but when properly recognized it responds well to treatment with stimulant medication and schedules that avoid sameness and repetition.