This ecological study examines trends in socioeconomic differentials in mortality in New South Wales, Australia, over a 20-year period (1970-89). The proportion unskilled was used as the indicator of socioeconomic status and its selection justified. Using census data aggregated by Local Government Area, the relationship between mortality and socioeconomic status was examined using quintiles based on the proportion unskilled in the population. Local Government Areas were also sorted into quintiles using mortality rates (0-74 years) to describe change in mortality differentials over time. Socioeconomic differentials were more evident in the relatively homogeneous Local Government Areas within the Sydney Statistical Division than in the remaining NSW Statistical Divisions which are more heterogeneous and predominantly rural. Although there has been an overall decline in mortality for males and females, and for high and low status groups, over this period the relative socioeconomic differentials have not declined. For the most recent period (1985-89) there appears to be some widening of differentials for males. The NSW state trends are generally similar to those reported for Britain and for other industrialised countries, suggesting that this is a common trend and that policies to reduce inequalities have not been effective.