Despite new improvements in AIDS treatment, preventive measures are still essential to control the epidemic. Effective programs almost always depend on correct and efficient allocation of scarce health resources. Detailed information on the epidemic, such as where, when, and how the epidemic will spread are of great value. This study was conducted to obtain a better understanding of the dissemination of AIDS cases in four important Brazilian States. Spatial diffusion patterns were evaluated qualitatively by studying sequential maps and quantitatively by analyzing spatial correlograms. Ten years were analyzed, grouped in three periods (1987-1989, 1990-1992, and 1993-1996). The diffusion process was studied for both total AIDS cases and male and female cases. Diffusion of AIDS cases presented specific characteristics for each of the four States. Information derived from the study, especially the results of the correlogram analysis, improve our understanding of the epidemic's spatial diffusion in different parts of the country and can also be used to determine parameters for other AIDS epidemiological models.