BACKGROUND Epidemiological studies have consistently demonstrated social inequality to be an important factor in the distribution of illness and death in society. However, little work has been published on social differentials in mortality in the world's developing countries, where socioeconomic contrasts are often considerably greater. METHODS In order to evaluate the extent of social differentials in mortality in a setting of major social inequality -- the State of São Paulo, Brazil, deaths in men aged 15-64 years residing in São Paulo from 1980 to 1982 were linked in broad, occupationally-determined categories to estimates of population size based on the 1980 Brazilian national census. The occupational categorizations utilized a Brazilian classification scheme and additionally that of the British Registrar General. RESULTS Mortality was 3.8 and 2.9 times greater comparing least to most socially favoured occupational category in each of the two classification systems, respectively. Independent of system, mortality decreased approximately 1.1% for each 1% increase along the occupationally-defined social gradient. This decrease was 48% greater than the equivalent calculated decrease for men of England and Wales. CONCLUSIONS These data support the contention that mortality for Brazilian adults, even more so than for adults of the world's more economically developed nations, is inextricably bound to the issue of social equity.