A survey was conducted in which 180 randomly selected male prisoners ages 18 to 44 were interviewed using the Diagnostic Interview Schedule and other questionnaires. A comparison was made with 1,006 similarly aged male residents of Edmonton who were interviewed using the same instruments. Compared to the general population, prisoners were less likely to be married and were less well educated. There was a higher proportion of Native Indians in the prison sample and lower proportions of Oriental and other racial groups. Prisoners were twice as likely to have a lifetime psychiatric disorder compared with the general population, and all individual disorders investigated were more common in the prison population. Six month prevalence showed even greater rates compared with the general population, indicating recent symptoms. The number of individual disorders per prisoner was also higher than for the general population. Lifetime suicide attempts were seven times more frequent in prisoners than in the general population.