Malignant stromal tumours of the duodenum are rare. The efficacy of surgical resection for duodenal leiomyosarcoma was assessed in 5 patients treated over an 11-year period, probably the largest series treated by a single surgeon. There were 3 women and 2 men with an age range of 27-52 years. Tumours were large (8.5-21 cm diameter) and partly cystic (4 cases). They arose from the second (2), third (2) and fourth parts of the duodenum. Resection was a major undertaking and comprised either partial duodenectomy (n = 4) or Whipple resection. Two patients required a right hemicolectomy in addition. Two patients with positive resection margins had adjuvant radiotherapy. Operative time ranged from 4.0 to 6.25 h and blood loss from 1.8 to 4.5 litres. Two patients developed complications: a transient low-output biliary fistula and an infected haematoma requiring percutaneous drainage. The 2 patients with incomplete resection died of recurrent disease at 3 and 15 months. The 3 survivors are free of disease at 24, 60 and 66 months. The results support a policy of aggressive resection despite the technical difficulties posed by these large and vascular tumours.