The United Kingdom's policy of opiate regulation consists of (1) competitive prescribing by hospital clinics, (2) control of the prescriber by limiting the prescribing of heroin and cocaine to licensed doctors who must conform to dispensing regulations set by the Government, (3) police and customs activity in reducing the availability of controlled drugs from illicit sources and the use of heavier penalties for offenses of unauthorized supply, (4) public education, and (5) the treatment of addicts to reduce the risk of detrimental influence on others. The available evidence suggests that for nontherapeutic addicts coming to notice between 1960 and 1975, addiction and criminal histories tend to run a parallel course. Addicts who have continued to receive prescriptions for opiates are more likely to be convicted of, or to admit to, offenses than those who have not; however, for males, apart from the number convicted exclusively of drug offenses, the number convicted (during 5 years of followup) has not exceeded the number for the general male population of similar age and number of previous convictions. The major effect of opiate use on criminal history is the increase in the number of drug convictions and in the number of persons convicted of such offenses. The drug offenses generally consist of supplementing prescriptions with additional amounts from illicit sources or preferring to use heroin rather than the methadone usually prescribed by the clinics. The relationship between opiate use and crime cannot be simply ascribed to the type of control policy. It is more likely to be the result of complex interaction between treatment practice, the availability of licit and illicit supplies, and the social security legislation. It probably also involves the characteristic level of crime in the community and the extent of public and political anxiety about drugs and crime. A total of 35 notes are listed.