OBJECTIVE Incidence of malignancy in solid organ transplant recipients is higher compared to the general population. The aim of this study was to characterize distribution and appearance of abdominal malignant tumors detected with spiral computed tomography (CT) examination in patients with solid organ transplantation. METHODS Between July 1994 and April 2006, 198 patients underwent liver transplantation and 568 patients underwent renal transplantation in our center. The abdominal CT studies were reviewed to determine the presence or absence of abdominal malignancy. All abdominal CT examinations were performed prior to immunomodulation or chemotherapy. RESULTS Eleven renal and one liver transplantation patient developed an abdominal malignancy. Among 11 renal transplantation patients eight were diagnosed as abdominal Kaposi's sarcoma (KS) and three as posttransplantation lymphoproliferative disorder (PTLD) upon spiral CT examination. In two patients the transplanted organ itself had malignant tumors: one patient had PTLD with Burkitt lymphoma in the transplanted liver and the other a renal cell carcinoma in the transplanted kidney. Abdominal PTLD and KS showed imaging findings and the site of organ involvement somewhat different from nontransplant patients. The most common pathologies in KS were liver lesions (n=6) and lymphadenopathy (n=6). But in abdominal PTLD, the spleen (n=3) was the most involved organ. CONCLUSIONS The early diagnosis of abdominal malignancies after solid organ transplantation is crucial for the patient's prognosis, especially under immunosuppression. The abdominal spiral CT examination was an effective modality to depict a malignancy among patients with solid organ transplantation.