In order to study differences in mortality and causes of death between HIV positive and HIV negative intravenous drug users (IVDU), 1009 (180 HIV positive and 829 HIV negative) IVDU in Oslo, Norway, were followed from their first HIV test for a mean period of 36 months (range 1-67 months). Eighty-seven (55 HIV negatives and 32 HIV positives) died during the follow-up period. The risk of death for IVDU was 31 times higher than for the general population. The estimated probability of survival after 3 years of follow-up was 0.92 for the whole cohort, 0.93 for the HIV negative group and 0.87 for the HIV positive group (P 30 years of age and > 5 years of IV drug use prior to study entry were all significantly associated with a fatal outcome. Eleven per cent (n = 20) of the HIV positives and 4% (n = 38) of the HIV negatives died from drug overdose, which accounted for 68% of all deaths; 2.2% of the HIV positives and 0.4% (n = 4) of the total cohort died from AIDS. Drug overdose represented the major threat to life among IVDU in this study. Because of the dynamics of the HIV epidemic, AIDS may have an increasing impact on mortality. However, in order to forecast the number of AIDS cases among IVDU the high non-AIDS mortality must be controlled for.