RESUMO
Desmoid tumors are rare, benign tumors with locally aggressive behavior which originate from fascial or musculoaponeurotic structure. They are more common in young women than young man. The etiology of desmoid tumors are uncertain but may be related to operation, trauma or hormonal factors. The authors report a 17-year old woman, gravida 1, para 1 with a mass at her lower abdominal wall during the fifth month of gestation. She was biopsied during delivery in another hospital but was not given a definite diagnosis. The mass had grown rapidly after biopsy and delivery. The tumor measured 28 x 21 x 18 centimeters in size and 4,900 g in weight. Complete surgical excision was performed The pathological report was desmoid tumor (aggressive fibromatosis). She had no post-operative complication and no recurrent tumor in the 8 months after operation.