There are reports of rare cases of malignant schwannoma of the small bowel, ovary or urinary bladder. We report a case of malignant schwannoma found in peritoneum without any other localisation in 66-year-old woman. The first diagnosis was tumor of right ovary. Laparotomy was performed and a big, solid tumor of urinary bladder involving the small bowel was found. There were some small tumors in peritoneum and parametrium. All the tumors were removed. The histological changes of the small lesions were described as malignant schwannoma. The mass in urinary bladder and small bowel was found to be of an inflammatory origin. The cases described by other authors suggest, that the diagnosis of malignant schwannoma in pelvis minoris is very difficult. Surgery is an adequate way of final diagnosis and management.