Sarcoma of the uterus accounts for less than 1 per cent of uterine neoplasms but is responsible for more than 15 per cent of deaths. However, histological or clinical malignancy features are poorly understood, in particular those which differentiate sarcomas from leiomyomas. This study involved 16 cases, seen during 8 years in two gynecology clinics in Iasi (Rumania) and chosen according to histological diagnosis. Ten leiomyomas were also chosen for comparison of symptomatology. The malignancy criteria studied--vascular invasion, cellular density, number of mitoses and histological type (most often leiomyosarcoma: 8 out of 16)--were used to compare sarcomas with suspect leiomyomas. The mean age was 50, 7 cases being diagnosed after the menopause. The commonest symptom was metromenorrhagia (11 cases out of 16), but pain was more frequent in leiomyomas (9 out of 10). Treatment was above all surgical, total hysterectomy having the best prognosis (3 deaths out of 8 patients operated upon). Other methods (in particular radiotherapy) not being used immediately after surgery, they could not be studied. In terms of its difficult diagnosis and its high degree of malignancy (9 deaths out of 16), sarcoma must remain an argument in favour of total hysterectomy.