The incidence of several cancers increases with height. Some studies report that leg length, a marker of prepubertal growth, is the component of height underlying these associations, but few prospective studies have investigated this issue. We examined height-cancer associations in a 21-yr follow-up of a cohort based on 2,512 men aged 45-59 living in the town of Caerphilly, South Wales, U.K., between 1979 and 1983. The men underwent a detailed examination, and 2,393 (95.3%) had measures of height and sitting height (from which leg length and trunk length were derived) recorded and were cancer-free at baseline. Cox proportional hazards models were used to investigate associations of height, leg length, and trunk length with overall and site-specific cancer incidence; 328 men developed cancer over the follow-up period. Associations with height were weak and did not reach conventional levels of statistical significance. In models controlling for age, socioeconomic position, smoking, and body mass index, cancer incidence was weakly positively associated with increases in height; hazard ratio (HR, 95% confidence interval) per standard deviation (6 cm) increase in height was 1.09 (0.97, 1.21; P = 0.14). Associations were somewhat stronger in relation to leg length (HR 1.09; (0.97-1.22) than trunk length (HR 1.05; 0.94-1.18). Height-cancer associations were strongest for lung cancer (HR 1.21; 0.96-1.51). This analysis provides limited support for the suggestion that leg length is the component of height underlying height-cancer associations