The annual rainfall distribution in São Paulo was studied based on data collected at 249 Tainfall stations scattered throughout the state (see map for localization of stations). Most of the data resulted from observations carried out during a period of 10 years, but data for longer periods, available for certain stations, were used for comparisons. According to the annual rainfall pattern, the state of São Paulo was divided in the following areas: 1) the coastal region, including S. Sebastião, Santos, Iguape, and Alto do Ribeira; 2) the plateau region (Planalto Paulista) comprehending the area between the Serra do Mar and the Paraná River; 3) the Mantiqueira Range and its adjascent area; 4) the Paraíba River Valley area with its specific rainfall pattern. Since this paper is intended primarily for agricultural use, the isohyets in the map were represented at intervals of 100 mm between 1000 and 1500; outside this range only the 1700, 2000, and 3000 isohyets were traced. The rainfall profile from Iguape to the Rio Grande, and from the state of Paraná to the Minas Gerais indicated that total rainfall and its seasonal distribution vary from the coast to the inland, and from Paraná to Minas Gerais. In both profiles the boundaries of the areas with a small winter rainfall were marked. The number of rainy days, the rainfall density, and the probable rainfall pattern for 30 stations chosen for the high reliability of the collected data were analysed, as well as the quotient of variation between the highest and lowest annual rainfall.