455 male and 120 female opiate addicts were treated at two London drug dependence clinics between 1968 and 1975. The delinquency pattern of 117 female addicts and of a systematic sample of 119 male addicts was analysed in relation to stages of their addiction career and outcome. Treatment had no effect on overall crime rate but there was a significant increase in the proportion of drug offences during the treatment stage. Comparisons between the sexes showed that the outcome of treatment was worse in women. In male addicts a history of delinquency had no prognostic significance, but in females convictions for non-drug offences before entering treatment might predict poor response to treatment of drug dependence.