Objective To analyze IMR evolution in the Sao Paulo Metropolitan Area (SPMA) between 1980 and 2000, in terms of spatial, age and, causal differences. Methods SPMA municipalities were divided into 5 groups, based on their 1980 IMRs: (3)90% lb (Group 1); 70-89% lb (Group 2); 50-69% lb (Group 3); <50% lb (Group 4). Group 5 comprised the municipality of Sao Paulo itself (IMR=51% lb). The analysis of trends was carried out using exponential regression models. Results IMR and its components showed a statistically significant decrease (p<0.05), with coefficients of determination between 66 and 98%, indicating goodness of fit of the exponential model to all the time series analyzed. SPMA IMR fell 69.4% from 55.2 to 169% lb, and Groups 1-5 showed reductions of 83.9%, 76.2%, 71.3%, 58.7%, and 68.8%, indicating that the groups with highest IMRs also showed the greatest reductions during the studied period. Conclusions IMRs were homogenized at around 18% lb in all municipality groups in the SPMA. One-half of all deaths were concentrated within the first week of life, and were due primarily to conditions originating in the perinatal period, indicating that greater care during the pre- and post-delivery periods will he required if the IMR in the SPMA is to descend to levels compatible with those of developed countries.