The prevalence of gall stone disease in a stratified random sample of 1896 British adults (72.2% of those approached) was established using real time ultrasound. The prevalence rose with age, except in women of 40-49 years, so that at 60-69 years, 22.4% of women and 11.5% of men had gall stones or had undergone cholecystectomy. The cholecystectomy rate of people with gall stone disease was higher in women than in men (43.5% v 24%, p less than 0.05). Very few subjects with gall stones had convincing biliary symptoms. In women, 10.4% had symptoms according to a questionnaire definition of biliary pain and 6.3% according to conventional history taking, while no men at all admitted to biliary pain. Nevertheless, cholecystectomy in men had nearly always been preceded by convincing biliary symptoms. The age at cholecystectomy was, on average, nine years less than the age at detection of silent gall stones in both sexes. It is concluded that either gall stones are especially prone to cause symptoms in younger people or that there are two kinds of cholelithiasis - symptomatic and silent. The lack of symptomatic gall stones in cross sectional surveys is probably due to their rapid diagnosis and treatment.