The aim of a cooperative study, carried out by the Paris Forensic Medicine Institute and the French National Institute of Health and Medical Research (INSERM SC8) was to assess the number of drug addiction-related deaths occurring in the Paris region in 1990. There were 253 deaths including 92 in Paris and 161 in Paris suburbs. A large percentage of these deaths were not recorded in the National death statistics registry (only 36% of all the deaths and only 24% of the Paris deaths had been registered). The overall drug addiction mortality in the Paris region is 29.4 per million inhabitants and is highest among the 25-29 year age group. Rates decrease rapidly after 30 years of age and are extremely low after 40. Mortality is highest in unmarried men and in the inactive population with a wide variability according to site of residence. Rates are much higher in Paris than in the suburbs. For the 20-29 year population in Paris, drug addiction has an important impact on the mortality figures for the general population, causing 12% of all deaths. It is the third cause of death after AIDS and suicide.