To determine maternal and fetal mortality associated with Eisenmenger's syndrome in the UK, a postal questionnaire was sent to 225 NHS obstetric units with neonatal intensive care units, requesting information about maternal and fetal outcome in cases of Eisenmenger's Syndrome between 1991 and 1995. Fifteen cases were identified. The maternal mortality was 40% and fetal loss 8%. Only 15% of infants were born at term. Maternal mortality associated with Eisenmenger's syndrome remains as high as it has been for the past 50 years. Pooling of national data on rare medical conditions in pregnancy is required to aid management of individual cases.