BACKGROUND Leiomyomas are benign smooth muscle tumors that usually arise from the uterus. METHODS We present a patient with a 6-month history of vague abdominal discomfort, occasional nausea, vomiting and urinary incontinence. On examination, there was an extremely large firm unpainfull palpable abdominal mass. Laboratory investigation revealed mild leukocytosis and blood creatinine elevation. Abdominopelvic ultrasonography and computed tomography revealed a massive well bordered, encapsulated intraabdominal tumor, extending from the pelvis to epigastrium and almost completely fulfilling the pelvic and abdominal cavity. At laparotomy, tumor arising from the retroperitoneum was excised in toto. Histopathological examination disclosed that the tumor was composed mainly of smooth muscle cells and very rare fibrous connective tissue elements with myxomatous alteration and with no mitotic activity. The negative results of numerous additional parameters analyzed (pancytokeratin, epithelial membrane antigen, S100 protein, CD68, CD34, desmin, aktin) ruled out different origin of a tumor. One year after resection the patient had no complaints and no radiological evidence of tumor recurrence. CONCLUSIONS Considering current limitations in radiological diagnosis, in toto resection of these tumors is necessary to rule out malignancy.