Studies have shown pathological gambling to be comorbid with substance use. Substance abusers experience gambling problems at much higher rates than the general population and are at greater risk of psychiatric disorders. This suggests that treatment for one condition should involve assessment and possible concomitant treatment for the other. Meta-analysis data have revealed lifetime rates of 5-33% in substance-abusing populations in industrialized countries, but there have been no relevant UK studies among these reviews. The UK national gambling surveys (2000-2007) have estimated the prevalence of problem gambling to be 0.6-0.8% in the general population. This study aimed to estimate the lifetime prevalence of problem gambling among a representative treatment-seeking sample of inpatients with diagnoses of alcohol and/or illicit drug dependence, and to compare this with estimates of problem gambling in the UK general population. It also aimed to investigate possible associations between demographics, criminality, severity of dependence, degree of impulsivity, severity of anxiety or depression and the presence of lifetime problem gambling in these individuals.