By September 30th 1991, 19,579 cases of AIDS among injecting drug users had been reported in Europe. HIV seroprevalence rates among drug injectors vary from less than 5% in some cities, to over 50% in others. Since the estimated number of drug injectors in Europe is between 750,000 and 1,000,000, HIV is a considerable threat to drug injectors, their sex partners and their off-spring, affecting large numbers of citizens in the European region. This paper gives an overview of the magnitude of the drugs/AIDS problem in the European region, and the concrete measures that have been taken to prevent HIV infection among drug users. Data from the evaluation of methadone programmes, needle and syringe exchange schemes and data on sexual behaviour change of drug users are critically reviewed. Limitations of the methods used for the evaluation of prevention activities are also discussed. Based on all the material reviewed, the main conclusions are the following: AIDS is a greater threat to public health than problem drug use, more accurate and reliable evaluation methods need to be utilized at European Community level, a combination of prevention measures should be used in order to reduce the further spread of HIV infection among injecting drug users.