Pyometra is a potentially lethal disease. Eighteen cases, all but one in postmenopausal women, were diagnosed at the Ottawa General and Ottawa Civic hospitals between 1974 and 1978 inclusive. A review of this series and of the literature demonstrates that a large proportion of cases (72% in this series) are associated with or follow radiotherapy for a malignant disease of the uterus and that anaerobic bacteria are frequently isolated from the uterine cavity (in 56% of the patients in this series). Because pyometra is potentially lethal (one patient in our series died) it should be considered as an abscess and treated promptly and vigorously by evacuation and continued drainage of the uterine cavity. Curettage of the cavity and the endocervical canal after dilatation is essential to rule out associated malignant disease as well as to debride the necrotic tissue. Antibiotics effective against aerobic and anaerobic bacteria should be given to all patients with signs of systemic infection. Once the infection is controlled, the underlying problem can be treated.