This study set out to determine the prevalence and predictors of warts in British schoolchildren by analysing medical examination data from a national birth cohort study of 9263 British children born 3-9 March 1958. The prevalence of visible warts, according to a medical officer, at the age of 11 was 3.9% (95% confidence intervals 3.5-4.3) and 4.9% (95% confidence intervals 4.5-5.4) at 16. Of the 364 children noted to have warts at the age of 11,337 (93%) no longer had warts at 16. Residence in the south of Britain, having a father with a non-manual occupation, being an only child, and belonging to an ethnic group other than white European were all associated with a decreased risk of visible warts. Region of residence was the strongest predictor of wart prevalence. There were no sex differences in wart prevalence. Warts represent a common source of morbidity in British schoolchildren. Future studies should take into account age, regional factors, social class, family size and ethnic group when comparing wart sufferers with other subjects.