The failure of fusion of splenic tissue results in the formation of accessory spleens. This entity normally appears in post-mortem examinations. The purpose of this work was to determine the incidence of the accessory spleen and to compare the ultrasonographic and tomographic features of the accessory spleen and the main spleen in a group of one thousand patients affected with several abdominal pathologies. Five hundred of these patients were studied by ultrasonography and five hundred patients by computed tomography. The ultrasonographic and tomographic features of the accessory and main spleen were similar. Its diagnosis is specially important in certain groups of patients with hematologic disease or abdominal trauma with splenic tear. This is due to the fact that the hypertrophy of the accessory spleen can produce a relapse of the disease.