There is frequently an increase in spleen size in infectious systemic and chronic venous congestion. The aim of this report was to perform a comparative study of the spleen tissue of chagasic or nonchagasic autopsied patients with or without congestive heart failure. Evaluations were made of 111 cases. Connective tissue intensity, follicular density and area, and follicular arterioles wall area were determined through the morphometric study. The connective tissue was similar in all groups. The density of the lymphoid follicles was significantly less among the chagasic cases (P = 0.032). The follicular area was larger among the chagasic cases and in the chagasic group with congestive heart failure. The chagasic group without congestive heart failure presented a greater area of follicular arteriole walls. Therefore, the spleen modifications in chronic Chagas' disease could be a consequence not only of the heart failure but also of the Chagas infection itself.