ADHD in children and adolescents is associated with substantial comorbidity. Longitudinal studies have shown ADHD to frequently persist into adulthood. OBJECTIVES: To use administrative data from Nordbaden / Germany to assess the extent of co-existing medical conditions in grown-ups with a diagnosis of ADHD (Hyperkinetic Disorder: ICD-10 F90.0, F90.1). METHODS: Using the comprehensive claims database of the official physicians' organization of Nordbaden (KVNB, with an insured population of 2.234m in 2003), n=630 ADHD patients age 20 and beyond were identified. The ADHD group was matched with a non-ADHD cohort (n=630) on a 1:1 ratio based on age and gender, and the rate of co-existent conditions was compared between both groups. Chi-square statistics was used to explore levels of significance. RESULTS: The most prevalent psychiatric conditions associated with ADHD in adults included depressive episodes (F32: prevalence 30.3%; relative risk [RR] 7.1*** [p<0.001]), recurrent depressive disorder (F33: 14.3%, RR 12.9***), persistent mood disorders (F34: 7.0%, RR 11.0***), anxiety disorders (F41: 15.7%, RR 5.8***), adjustment disorders (F43: 18.9%; RR 6.6***), other neurotic disorders (F48: 8.6%, RR 6.8***), specific personality disorders (F60: 14.1%; RR 22.3***), other behavioral/emotional disorders with onset in childhood/adolescence (F98: 9.0%; RR 57.0***), mental/behavioral disorders due to substance use (F19: 4.9%; RR 7.8***) or due to use of alcohol (F10: 4.6%; RR 5.8***), and eating disorders (F50: 4.3%, RR 13.5***). Non-psychiatric conditions associated with ADHD included obesity, metabolic, infectious and allergic disorders, including asthma bronchiale, and diseases of the ear and hearing loss but not disorders of the eye and visual disturbances. Detailed analyses by age and gender will be presented. CONCLUSIONS: These data point to significant comorbidity associated with ADHD in grown-ups, thus underscoring the clinical relevance of the condition. They provide a basis for further epidemiological research and for analyses of the cost associated with ADHD in adult patients.