Whereas the adverse impact of attention-deficit/hyperactivity disorder (ADHD) on emotional and psychosocial well-being has been well investigated, its impact on physical health has not. The main aim of this study was to assess the impact of ADHD on lifestyle behaviors and measures of adverse health risk indicators. Subjects were 100 untreated adults with ADHD and 100 adults without ADHD of similar age and sex. Unhealthy lifestyle indicators included assessments of bad health habits, frequency of visits to healthcare providers, and follow through with recommended prophylactic tests. Assessments of adverse health risk indicators included measurements of cardiovascular and metabolic parameters, weight, body mass index, and waist circumference. No differences were identified in health habits between subjects with and without ADHD, but robust differences were found in a wide range of adverse health risk indicators. ADHD is associated with an adverse impact in health risk indicators well known to be associated with high morbidity and mortality.