PURPOSE: To characterize the imaging features of desmoplastic small round cell tumor of the abdomen and correlate them with the histopathologic findings. MATERIALS AND METHODS: Eleven of 14 patients with desmoplastic small round cell tumor had primary abdominal involvement. In nine of these patients (mean age, 20 years), results of imaging studies (computed tomography in nine patients, ultrasonography [US] in three) and histopathologic specimens were retrospectively analyzed. RESULTS: The hallmark imaging feature was lobulated peritoneal masses (mean number, 4.4; range, 1-17) with a mean diameter of 5.0 cm (range, 2-12 cm). Omental and paravesical tumors were each present in six patients. Retroperitoneal masses were present in three patients. The tumors were well defined and hypoechoic at US. Heterogeneity due to tumor hemorrhage or necrosis was seen in seven patients. Ascites was present in five patients. Parenchymal and/or serosal hepatic metastases, punctate calcifications, nodular peritoneal thickening, lymphadenopathy, hydronephrosis, and bowel obstruction were less common associated findings. CONCLUSION: Bulky peritoneal soft-tissue masses without an apparent organ-based primary site are characteristic of intraabdominal desmoplastic small round cell tumor. Although the findings are nonspecific, this diagnosis can be considered in adolescents and young adults with characteristic imaging findings.