A study of 4.652 schistosomiasis mansoni patients from 18 different States in Brazil, indicates a general picture of the morbidity of this disease in the country. Patients migrants (4.652) from different States were studied in the Department of Tropical Medicine of Federal University of Rio de Janeiro, between 1960 and 1979, with the following parameters: selected by a positive stool examination (sedimentation technique), clinical and epidemiological evaluation to determine the clinical form, migration pattern, age, sex and race. A routine chest X ray, E. C. G., haematologic and biochemistry tests, were performed. In a selected group of hepatosplenic cases a liver, biopsy, splenoportography and a portal hemodynamic study were done. Although some regional, familial, racial and/or individual differences in morbidity have been observed, the intensity of the primary infection and reinfections in the first two decades of life seems to be most important factors in the severity of human infection in Brazil. A direct correlation between egg out put and disease severity was observed in patientes under 30, except in negros who almost always present a mild form of the disease regardless of parasite burden. The evolutive pattern of the disease should be crefully investigated in relation to adaptation of different strains according to the host's immunological reactions and genectic constitution.