The aim of the study was to investigate the association between social and behavioural factors, and the use of different types of drugs in a cohort of 8168 Swedish men conscripted for military service in 1969-70. Data about social and behavioural characteristics, self-reported use of alcohol and narcotics was obtained from a survey of all Swedish conscripts. Information on intravenous drug abuse up to 1970 was obtained from a survey of injecting males among persons brought to the central police arrest. A higher proportion of intravenous drug abusers than cannabis abusers came from social class III, had divorced parents, had been in contact with the police and juvenile authorities, and had low emotional control. Indicators of deviant behaviour, e.g. truancy, having run away from home, and contact with police or juvenile authorities, were associated with high odds ratios for intravenous drug abuse and for cannabis abuse. In multivariate analyses, these risk factors still carried significantly increased odds ratios. In general, the odds ratios associated with these background factors were higher for intravenous drug abuse than for cannabis abuse. The risk increased, however, with increasing level of cannabis abuse. In conclusion, poor social background and deviant behaviour was strongly associated with future intravenous drug addiction, whereas the association was much weaker in the case of future cannabis abuse.