PURPOSE: To evaluate the dual-phase bolus CT findings and clinical significance of splenic S. O. L.(SpaceOccupying Lesion) basically included in abdominal CT but previously not considered important. MATERIALS AND METHODS: We retrospectively reviewed 64 splenic S.O.L.'s(0.94%) detected among 6842 patients who underwentdual-phase rapid sequence abdominal CT. Diffuse splenomegaly and heterogeneous enhancement during the arterialphase were excluded. Fifty-eight of 64 splenic S. O. L. cases were confirmed by surgery, biopsy, radiologic studyand follow up. RESULTS: In only eight patients(12.5%) were symptoms localized to the left upper quadrant. Therewere 21 cases of inflammatory and ischemic diseases(36.2%), 19 malignant tumors(32.8%), 12 benign cysts(20.7%),four benign tumors(6.9%), one metabolic disease and one hematoma(each 1.7%) ; six cases were not confirmed and inthese, S.O.L. was also found at other sites. Escept in the case of benign cysts and tumors, the early phase wasbetter than the late for the detection of S.O.L., though both were good for diagnosis. Among 21 inflammatory andischemic lesions there were eight cases of portal hypertensions, seven of pancreatitis, and one of tuberculosis ;five were due to other cauese. Among 19 patients with malignant tumors, metastases were most common(11 cases).Cases involving malignancy involved four lymphomas, two cases of leukemias and two angiosarcomas, which togetherrepresented only primary splenic malignancy. Two epidermoid and ten simple cysts were benign, while benign tumorsincluded three hemangiomas and one lymphangiomatosis ; these were difficult to differentiate from angiosarcoma.Gaucher's disease showed multiple low density lesions in the enlarged spleen and one hematoma was also present. CONCLUSION: Splenic S.O.L.'s are very rare and clinical symptoms directly related to splenic mass are uncommon.Benign and secondary lesions are more common than malignant and primary lesions, and cysts are also much rarerthan any other solid organs. Dual-phase CT especially during the early phase, is currently the modality of choicefor the evaluation of splenic S.O.L.