The usual imaging findings of common splenic infarction are well known, while the findings for splenic infarctions in the accessory spleen or polysplenia are rare; these unusual imaging findings may make the diagnosis difficult. We report here on two patients who have complained of abdominal pain, and they were diagnosed as splenic infarction that developed in either the accessory spleen or as has having polysplenia. We can diagnose splenic infarction that unusually develops in the accessory spleen or polysplenia when we identify a round, hyperechoic, avascular solid mass on US, or when we identify a round, rim-enhancing, hypodense solid mass with adjacent inflammatory changes and a small amount of ascites on CT that is adjacent to the normal spleen or in one of splenules of polysplenia in the clinical settings of acute abdominal pain.