Desmoplastic small round cell tumor (DSRCT) is a rare and highly aggressive neoplasm, which predominantly affects young males. We report a case of DSRCT affecting an 11-year-old male patient, with intra-abdominal involvement characterized by a large retroperitoneal mass in left hypochondrium. Histological examination of the mass showed the presence of clusters of small blue round tumor cells surrounded by a dense desmoplastic stroma. Immunohistochemical analysis disclosed a positive reaction to desmin, WT-1 and cytokeratins. After diagnosis, the patient underwent chemo radiotherapy treatment, but died at the 24th month of follow-up.