The aim of this study was to assess the prevalence of alcohol dependence and anxiety and depressive disorder symptomatology among heroin users in drug treatment. Fifty-five clients on methadone maintenance treatment programmes in Dublin were interviewed. Prevalence rates were found to be 56% [n=31] for alcohol dependence, 56% [n=31] for anxiety disorder symptomatology, and 42% [n=23] for depressive order symptomatology. This finding of comorbid alcohol dependence and psychopathology among methadone maintenance treatment clients suggests that both clients' health and methadone maintenance treatment participation and completion rates may be compromised. The author concludes that alcohol dependency and psychopathology among methadone maintenance treatment clients should be considered when providing effectively targeted services to the drug using population.