Forty-six patients with smooth muscle tumours of the stomach and small intestine were treated surgically at the Princess Alexandra Hospital between 1970 and 1986. Leiomyomas were three times more common than leiomyosarcomas, but malignant tumours occurred more frequently in the small intestine than in the stomach. Gastric tumours tended to present with gastrointestinal bleeding, in contrast to intestinal lesions which presented predominantly with abdominal pain. Although leiomyomas tend to be smaller at operation than leiomyosarcomas, the size of a smooth muscle tumour is not reliable in discriminating between benign and malignant lesions. Therefore all smooth muscle tumours of the upper gastrointestinal tract should be excised as widely as possible, including local lymphatics in the dissection where practicable, so as to maximize the likelihood of radical extirpation of malignant lesions. Approximately one-third of patients with leiomyosarcomas have metastases at the time of surgery; the 5 year survival rate after surgical treatment of leiomyosarcomas of the upper gastrointestinal tract is less than 50%.