The incidental finding of tumor-llke perirenal or renal splenosis (PRS) creates a challenge to the renal physicians, because its benign nature has to be distinguished from a malignancy. This paper describes the case of a 40-year-old man referred from a local clinic for further evaluation of an incidental finding of left abdominal masses by ultrasonogram suspecting neoplasm, but was eventually confirmed as PRS by obtaining a history of splenectomy that pointed to splenosis and subsequently by a fusion image from single photon emission computed tomography using 99mTc-labelled heat-denatured erythrocytes and computed tomography (hybrid SPECT/CT). In addition, a review of 27 cases of PRS in a MEDLINE search including the present case revealed the following: all the masses were found incidentally and were associated with a history of previous splenectomy or splenic injury; the initial impressions were neoplastic tumor/PRS (n = 9), PRS (n = 10), and neoplastic tumor without consideration of splenosis (n = 8); surgical exploration was undertaken in all the 8 cases of suspected neoplastic tumor only, whereas non-invasive radiological or radionuclide imaging confirmed splenosis in the rest of the cases (n = 19). To avoid unnecessary tests and invasive surgery for undetermined perirenal or renal masses accompanying previous splenic injury, we stress the paramount importance of careful history-taking, physical examination, and a high index of suspicion for splenosis. Also, fusion imaging of hybrid SPECT/CT was reconfirmed as a useful diagnostic technique for accurately detecting and localizing splenic tissues by PRS.