Peptic ulcer prevalence and five year incidence were assessed in a sex and age stratified population sample of 3608 Danish subjects aged 30-60 years. Statements of peptic ulcer disease obtained from questionnaires were scrutinised by reviewing medical records. Life time ulcer prevalence (95%/o confidence intervals) was 5.6 (4.9-6.4) per cent. Male to female prevalence ratio was 22:1, and duodenal to gastric ulcer prevalence ratio was 3.8:1. Thirty two participants with no previous history of peptic ulceration developed an ulcer within the observation period resulting in a five year ulcer incidence of 11.3 (7.4.15.2) per 1000 persons at risk with no demonstrable sex difference. The prevalence of duodenal ulcer has declined in Denmark whereas gastric ulcer prevalence in men has increased slightly. A decline in male duodenal ulcer incidence has probably contributed to the low male to female ulcer incidence ratio, implying that women today incur the same risk of developing an ulcer as men. continue, they will bring about a new era in ulcer epidemiology characterised by equal incidence in men and women and an even distribution of lesions in the stomach and duodenum. (Gut 1995; 36: 819-824) Keywords: peptic ulcer, duodenal ulcer, gastric ulcer, epidemiology, prevalence, incidence.Since the mid-twentieth century peptic ulcer mortality in Westernised countries has declined in young and middle aged subjects. Ulcer mortality in senior citizens has, none the less, remained essentially unchanged or even increased.' Similar trends have been seen when other frequency estimates of ulcer occurrence such as hospitalisation, operation, and physician visit rates have been reviewed.2 Assessment of true peptic ulcer rates do, however, pose several methodological problems.3 Preferably prevalence and incidence rates should be based only on cases verified by endoscopy, roentgenograms or surgery. Gastric and duodenal ulcer rates should be reported separately and ulcer incidence calculated exclusively from first time verified lesions.As ulcers are present intermittently, simply performing endoscopies on a representative sample of subjects does not ensure valid estimates of ulcer occurrence. Consequently, most previous studies have used hospitalisation rates and mortality as approximate measures of overall ulcer occurrence. Those findings are probably impaired by selection bias. Self reported ulcer occurrence likewise could be prone to bias. Provided that an unselected population is used, however, such an approach does have several advantages making it the most suitable means of determining the prevalence and incidence of peptic ulceration.This study reports the lifetime prevalence and five year incidence of peptic ulcer disease in an unselected Danish population. Ulcer incidence was computed exclusively from ulcer episodes occurring among participants with no previous history of peptic ulceration at study entry. Furthermore, ulcers were classified according to location whenever possible. Index cases were those who claimed tha...