In a series of 412 patients with Klinefelter's syndrome observed over periods ranging from 1 to 20 years, the frequency of hypostatic ulceration, deep vein thrombosis and pulmonary embolism was found to be raised. The prevalence of past or present hypostatic ulceration was 6%, which is 20-50 times higher than in the general population. The incidence of deep vein thrombosis in subjects aged between 30 and 70 years was 22.8 cases per 10,000 patient-years at risk. In community studies the incidence of this condition is around 4 new cases per 10,000 men per year. The frequency of pulmonary embolism was 16 cases per 10,000 patient-years at risk, compared with an expected figure of 0.9 to 3 cases per 10,000 men per year.