BACKGROUND The estimated prevalence for attention-deficit hyperactivity disorder (ADHD) in adulthood is 2 - 6 %. Patients with a substance use disorder met the criteria for ADHD between 30 and 50 %. ADHD and conduct disorders are discussed to increase risk of developing substance abuse and increase severity of disorder. METHODS We compared epidemiological and clinical characteristics and comorbidity in subgroups of 314 adult alcoholics of German descent with or without persistent symptoms of attention-deficit hyperactivity disorder (ADHD). Aim of the study was to identify specific pathophysiological mechanisms that could contribute to vulnerability, severity or complication of alcohol dependence. RESULTS 21.3 % of the alcoholics fulfilled DSM-IV-criteria of ADHD with ongoing symptoms in adulthood and had a Wender-Utah-Rating-Scale score > 90. Subgroup of alcoholics with ADHD were significantly younger at age of onset of alcoholism (24 years versus 30 years), had a significantly higher daily alcohol intake (253 g versus 196 g EtOH), had significantly more social stress, lifetime experiences in court proceedings against them (11 versus 2 %) and suicidal ideation (25 versus 11 %). In the subgroup of alcoholics with ADHD 51 % fulfilled criteria of antisocial personality disorder. The early onset of alcoholism was most pronounced in this subgroup. CONCLUSIONS In our sample, persistence of ADHD symptoms from childhood into adulthood and antisocial personality disorder contributes to vulnerability and morbidity of alcohol dependence with early onset and greater severity of disorder.