Following the worsening of drug-addiction problems during the 1980s, Switzerland started to apply a diversified drug policy based partly on the harm reduction approach. In this context, a program of medical prescription of opiates — including heroin — started, on an experimental basis, in 1994. Eligibility was limited to drug addicts over twenty years of age, who had been using illegal drugs for at least two years, displayed signs of health or social deterioration, and for whom other treatments had failed. An evaluation was performed on the effects of the program on criminal involvement of the subjects treated. In the evaluation, several measures were used to compare offence rates before and during the prescription period, namely: records of convictions, police records and extensive interviews (conducted every six months) using instruments measuring self-reported delinquency and victimisation. The results showed substantial drops in the prevalence and incidence of delinquency. The rates of victimisation presented a similar reduction. It was also shown that delinquency and victimisation are closely related.