This survey was a sub-study of the Prevalence Project, the collective name for several studies undertaken to determine prevalence of drug use in Sweden. This sub-study was a large-scale postal survey of a stratified sample of 58,000 individuals randomly selected from all registered inhabitants of Sweden. There were 22,095 respondents (response rate of 38.3%, or 52.1% weighted). Individuals surveyed were ages 15-64. Survey response data were also linked to registry data to obtain information on education, income, marital status, and other variables.