Mortality and causes of death in Crohn's disease. Review of 50 years' experience in Leiden University Hospital. Six hundred and seventy one patients (52.5% women) with Crohn's disease seen at Leiden University Hospital between 1934 and 1984 were identified. Follow up was 98.2% complete. Sixty four (9.7%) of the 659 patients died. The cause of death was related to Crohn's disease in 34 patients, probably related to the disease in four, and unrelated, from incidental causes, in 25. The cause of death could not be identified in one patient. There was a significant decrease of deaths related to the disease after 1973. Causes of death such as amyloidosis and malnutrition have disappeared and postoperative deaths have decreased. The standardised mortality ratio showed an excess mortality of 2.23 for all patients. It was higher for women (3.30) than for men (1.76). A comparison of two recent 10 year periods showed a significant decrease in standardised mortality ratio in men but not in women. Patients whose disease started before the age of 20 years had an excess mortality compared with older patients. This study supports the view that the prognosis of Crohn's disease has improved in general but high quality medical and surgical management is important particularly for younger patients. 