Objectives: To study the trend in mortality from 1980 to 1991 in a cohort of 2432 intravenous drug users (IVDU) enrolled between 1 November 1980 and 31 December 1988. In addition, to evaluate the impact of HIV-1 infection on mortality.

Design: The vital status of people enrolled in the cohort was ascertained at registry offices of the municipalities of residence. Cause of death was determined by reviewing death certificates, clinical records and autopsy reports. Within the cohort, the causes of death of HIV-1-infected subjects were compared with those of subjects of undetermined serologic status.

Setting: Municipalities of the metropolitan area of Milan.

Results: The cohort was followed-up for 16415 person-years (PY) and 413 deaths were observed up to 30 June 1991. Mortality was 25.2 per 1000 PY, 20.5 times greater than that of the general population of the same age and sex. The leading cause of death was drug overdose, followed by AIDS (death rates 9.2 and 8.8 per 1000 PY, respectively). Mortality remained under 16 per 1000 PY from 1981 to 1986, and then increased rapidly to 63.8 per 1000 PY in the first half of 1991. AIDS and overdose accounted for most of this increase, with AIDS becoming the leading cause of death from 1989. Mortality in HIV-1-infected IVDU was higher than in IVDU as a whole (48.0 versus 19.9 per 1000 PY), and the difference was entirely due to AIDS and infectious diseases.

Conclusion: The overall mortality rate and the mortality for AIDS and overdose were markedly higher than in other European countries in the same risk group. HIV-1 infection does not appear to affect the mortality for causes other than AIDS and infectious diseases.