A case of non-Hodgkin's lymphoma (NHL) involving the prostate and the urinary bladder in a 24-year-old male is reported. Although none of the currently available imaging modalities is specific for the diagnosis of NHL of the prostate, this diagnosis must be considered because of its amenability to treatment. The heterogeneity of the mass at CT and MRI might be suggestive of high-grade NHL. The patient was treated with intensive combination chemotherapy.