Incidence of gallstones in a Danish population. Five-year incidence of gallstone disease was assessed by ultrasonography in an age- and sex-stratified random population of Danish origin aged 30, 40, 50, and 60 years. The response rate was 82.8% (2987/3608). Nonrespondents did not differ from respondents regarding variables concerning gallstone disease. The 5-year incidence of gallstone disease in men aged 30, 40, 50, and 60 years was 0.3%, 2.9%, 2.5%, and 3.3%. Corresponding figures in women were 1.4%, 3.6%, 3.1%, and 3.7%. The incidence of gallstones was significantly higher in subjects aged 45 years or more compared with those aged 35 years. The sex difference in gallstone incidence decreased with increasing age. A significantly higher incidence of gallstone disease was found among subjects with former polyps in the gallbladder. Spontaneous disappearance of gallstones was seen in 4.5%. 