Mortality was studied among 348 males and 433 females who had or who carried the gene for the fragile X syndrome. The average age of death was about 12 years lower than in the general population for both men and women but this was likely a bias of ascertainment. The commonest causes of death were cardiovascular, cerebrovascular and malignant disease similar to those in the general population. No evidence for any specific disease susceptibility was found in this preliminary study.