BACKGROUND: Primary tumors in the presacral (retrorectal) space are extremely rare in adults, with an estimated incidence of 0.0025 to 0.014 in large referral centers. Congenital varieties are most common and comprise two thirds of these tumors. Primary retroperitoneal sarcomas in the pelvic region are extremely rare. We report the ultrasound and the corresponding Computed Tomography (CT) features of a rare presacral fibrosarcoma in an adult woman, in whom the diagnosis was confirmed by a CT-guided biopsy. CASE REPORT: A 54-year-old woman presented with a history of lumbar and perineal pain and painful defecation. Rectal examination revealed a hard mass in the retrorectal space. The patient was referred for imaging and a laboratory evaluation with a clinical diagnosis of a presacral mass. An abdominal ultrasound was followed by laboratory evaluation of routine hematological and hepato-renal parameters, abdomino-pelvic CT and a CT-guided biopsy. The imaging studies showed a presacral solid mass with nodular calcifications. There was conspicuous absence of cystic or adipose contents and of sacral erosion/destruction. However, hepatic metastasis was present.All imaging features suggested a retroperitoneal sarcoma in the pelvic region with metastases to the liver. The diagnosis was confirmed by CT-guided biopsy. CONCLUSIONS: We are reporting a new case of a very rare entity, a presacral fibrosarcoma. The imaging approach and the analysis leading to an appropriate differential diagnosis and final diagnosis is highlighted in our case report.