In this report we present the results of an epidemiologic survey performed in a low income urban neighborhood. The study was designed to investigate the prevalence of type II diabetes mellitus (DM) and impaired glucose tolerance (IGT) in this socioeconomic stratum. The study was done using the standard procedure for the oral glucose tolerance test (OGT) and the recommended diagnostic criteria for defining DM and IGT according to the World Health Organization. A neighborhood corresponding to a census tract was selected and defined by a map. The 39 blocks encompassed in the neighborhood were identified and randomized using the statistical package Systat. According to the randomization, a complete household enumeration was performed. All the residents and the family relationships were identified. The individuals that were between 35-64 years of age and were not pregnant, were considered eligible and were interviewed at home and invited to have a physical examination with an OGT. The number of inhabitants in the study was 4411 of whom 931 were eligible: 452 (48.5%) men, 479 (51.5%) women. The response rate for the home interview was 91.7%; for the physical examination with the OGT it was 69.8%. The crude rate prevalence of DM for men was 10.6%, and for women it was 14.8%. The crude rate prevalence of IGT for men was 12.8% and 12.3% for women. These results show that susceptibility to DM and IGT is high in our population and are among the highest in the world.