Pseudomyxoma peritonei or mucinous neoplasm of the appendix is a rare clinical condition characterized by the presence of mucinous ascites in which gelatinous material accumulates throughout the peritoneal cavity and pelvis. It usually arises from cystic neoplasm of appendix, ovary and rarely from colon. A 45 year old man presented with right sided abdominal lump and distension. Ultrasound and Computerized tomography diagnosed it as a case of psoas abscess with multiloculated heterogeneous echoic contents. Intraoperatively jelly like material was removed from retroperitoneum. Histopathological examination revealed features suggestive of mucinous adenocarcinoma. Aim in presenting this case is to increase the awareness among clinicians about the rare presentation of pseudomyxoma retroperitonei as a psoas abscess.