The proximate and evolutionary causes of the levelling of mortality rates at late ages, observed in several species, remain obscure. To investigate the causes of mortality levelling late in life in Drosophila melanogaster, we examined the effect of reproduction on mortality patterns, by conducting population cage experiments with a total of more than 45 000 individuals. Several different genotypes of reproducing and non–reproducing males from F1 crosses among isogenic lines were studied. Our results suggest that significant mortality levelling can occur even in non–reproducing males, but that reproduction also significantly affects mortality patterns. The results show that mortality levelling is strongly affected by the Gompertz initial mortality rate and exponential rate of increase parameters, probably through the effects of hetero geneity in mortality risks.