A database containing details of every incident of suicidal behaviour on the London Underground railway system between 1940 and 1990 was assembled from the records of London Underground Ltd and the British Transport Police. The total number of cases was 3240. The mean annual number of suicidal acts on the London Underground system increased from 36.1 (1940-1949) to 94.1 (1980-1989). There were significantly fewer incidents on Sundays than on the other days of the week and the daily rate was highest in the spring. 64% of incidents involved males and the peak age group for both sexes was 25-34 yr. Suicide verdicts were returned for a greater proportion of women than men. Overall case fatality was 55%. However, case fatality rates differed between stations, environmental factors appearing to influence survival. Possible strategies to prevent railway suicides and reduce the lethality of this method are discussed.