Aims. Assessment of prevalence of non-fatal overdoses and suicide attempts and predictors of and co-variation between such behaviours among drug addicts. Design. Cross-sectional survey. Setting. Inpatient and outpatient treatment units in Norway. Participants. National sample of 2051 drug addicts admitted to treatment in Norway in 1992-93. Measurements. Self-reports of suicide attempts and of life-threatening overdoses from structured interviews with therapists. Findings. Almost half (45.5%) the clients reported having experienced one or more life-threatening overdoses. A third (32.7%) reported one or more suicide attempts. Suicide attempts were more often reported among those who had overdosed (odds ratio (OR) = 6.3), and the number of life-threatening overdoses and number of suicide attempts were positively and moderately associated (Pearson's r = 0.39). Drug addicts who had exhibited both life-threatening behaviours were characterized by polydrug use, poor social functioning and HIV risk-taking behaviour. Suicide attempters were also characterized by psychiatric problems. Conclusions. The substantial co-variation between suicide attempts and drug overdose suggests some common underlying causal factors. These seem to be related to heavy drug use and poor social integration.