Background: Because autoimmune pancreatitis is a new disease entity, there are no data with regard to its prevalence.
Methods: To estimate the number of patients with autoimmune pancreatitis in Japan, we randomly selected hospitals using stratification and asked them how many patients they had with pancreatitis in 2002 who fulfilled the diagnostic criteria for autoimmune pancreatitis as proposed by the Japan Pancreas Society.
Results: The number of patients with autoimmune pancreatitis who visited hospitals in Japan in 2002 was approximately 900 (95% confidence interval; range 670-1100). The male : female ratio was 2.85 : 1, and the age of disease onset in 95% of the patients was over 45 years.
Conclusions: The prevalence of patients with autoimmune pancreatitis in Japan was estimated to be 0.82 per 100,000. Autoimmune pancreatitis was predominantly seen in men past middle age (over the age of 45 years).