The purpose of this work is to analyze the epidemiological changes that have occurred in São Paulo due to geographical and historical influences. This research was made during the period of 1963 to 1977, covering 6,664 cases and two main aspects: origin and age. In 1977, Sao Paulo presented 5,179 inhabitants per square kilometer and a percentage of 5,3 hanseniasis patients per square kilometer. The data compiled during the research have led to the following conclusions: São Paulo has become an important economical center and as such a point of attraction to intense migratory currents; this increase has caused the formation of unplanned and outnumbered populational centers in the outskirts which are obstacles to medical and social welfare assistance and to diagnosis and control as well; changes in the social and economical structures leading to a poorer family life; increase in the possibilities of transmission of hanseniasis either by non-intimate or long-termed contacts; decrease in the number of cases in the same family and, finally, the characterization of hanseniasis as a grown-up and urban disease.