OBJECTIVE The aim was to follow the time trends of mortality from ulcerative colitis and compare them with those of gastric and duodenal ulcer. METHODS Mortality data from 21 different countries between 1941 and 2004 were analyzed. The age-specific death rates of each individual country, as well as the average age-specific rates of all countries, were plotted against the periods of birth and death. RESULTS The average trends of mortality from ulcerative colitis, gastric and duodenal ulcer reveal distinctive and unique birth-cohort patterns of all three diseases. Similar to both types of peptic ulcer, the risk of developing ulcerative colitis started to rise in successive generations born during the second half of the 19(th) century. It peaked shortly before the turn of the century and has continued to decline since then. The rise and fall in the occurrence of ulcerative colitis preceded those of both ulcer types. CONCLUSIONS The birth-cohort pattern indicates that exposure to the relevant risk factors of ulcerative colitis occurs during early life. As the model of H. pylori and its associated birth-cohort patterns of gastric and duodenal ulcer suggest, an enteric infection provides a possible explanation for such temporal trends of ulcerative colitis as well.