A 5-year-old, female red-tailed boa constrictor ( Boa constrictor constrictor ) was presented with hyporexia, regurgitation and progressive focal distention of the caudal coelom since two months. During physical examination a firm, well-demarcated and movable intracoelomic mass was detected halfway down the caudal coelom but no other abnormalities were noticed. Ultrasonographic examination showed the mass to consist of an intestinal intussusception. A complete blood cell count and serum biochemistry blood test results revealed mild anemia and leukocytosis as well as hyperuricemia and hyperphosphatemia with inversion of the calcium/phospohorus ratio. Explorative coeliotomy was performed and revealed anterograde invagination of the ileum into the colon through the ileocolic junction. Although the intussusception was surgically repositioned, the snake died three weeks post-operatively despite showing a good general condition and defecation following assisted feeding. During necropsy, a thickened wall of the caudal segment of the ileum that was previously involved in the intussusception was observed as well as the presence of multifocal, white nodules throughout the parenchyma of the liver, spleen and kidneys. Histopathological examination demonstrated a malignant round cell tumor of the ileum with infiltration of neoplastic round cells in the liver, spleen and kidneys. Immunohistochemical staining (CD3, CD20, MAC387, S100 and NSE) could not confirm the cell origin of the round cell tumor. The present case highlights the need to include round cell tumors as a differential diagnosis in the development of ileocolic intussusception in red-tailed boa constrictors.