A study of morbidity was made among 510 patients with positive serology for Chagas' disease, originating from various states in Brazil. The study began in 1960 when the patients were submitted, in Rio de Janeiro, to clinical, electrocardiographic and radiological examinations as well as to serological, xenodiagnostic and other serial laboratory tests. The patients were classified according to their clinical state as: asymptomatic (indeterminate form), cardiac, and carriers of "megas" or associated clinical forms. The prevalence of cardiopathy was 52.1% and of "megas" was 14,3%. An association of cardiopathy and "megas" was observed in 10.7% of the patients whereas the association of megacolon and megaesophagus appeard in 10.9% of the cases. The indeterminate form (asymptomatic) was observed in 39% of the patients. The proportion of cardiopathic cases increased progressively between the first and the fifth decade of life, whereas the proportion of "megas" increased until the 7th decade. However, the highest number of cases in both forms appeard during the 4th decade of life. No significant differences were observed among the clinical forms by sex, in spite of a discrete predominance of cardiopathy in the male and of "megas" in the female. In relation to the patient's race (whites, blacks and of mixed race, it was not possible to observe a significant correlation with the different clinical forms since constitution of the cohort's origin was unknown. Even if the smal number of cases cannot be considered as representative of the clinical form prevalent in the area of origin, using te data of the four states with the larger number of cases, we observed that the proportion of cardiopathy/"megas" was respectively 65.7% and 20.1% in Bahia, 55.7% and 14.7% in Minas Gerais, 50.9% and 15% in Pernambuco and 23,.% and 0% in Paraíba. The small number of cases from the other states didi not permit any estimation of the proportion of every clinical form.