Yersinia enterocolitica infection is a zoonosis with worldwide distribution, gastroenteritis being by far the most common clinical manifestation of human infection. In Gipuzkoa, northern Spain, human Y. enterocolitica infections increased from the mid-1980s to the beginning of the 21st century (from 7·9 to 23·2 annual episodes per 100 000 population) to decrease to 7·2 annual episodes per 100 000 population in the last years of the study. The hospital admission rate due to yersiniosis during the last 15 years of the study was 7·3%. More than 99% of isolates were serotype O:3. Infection affected mainly children under 5 years of age (average rate: 140 episodes per 100 000 population). The incidence in adults was low but hospitalisation increased with age, exceeding 50% in people over 64 years old.