Idiopathic pulmonary fibrosis (IPF) has an unknown etiology and poor prognosis. Several large-scale epidemiological studies have been conducted predominantly in Western countries. There are few studies reported from Asian countries. It remains unclear whether ethnic difference exists in IPF. It is important to determine the current IPF status in Asian populations and compare it with that of Western populations.

Objectives: To provide the epidemiological status of IPF in Japan and to investigate ethnic differences.

Methods: We selected Hokkaido prefecture (population, 5.6 million) as the epidemiological cohort of IPF among Japanese. On the basis of the clinical records of 553 IPF patients who were accepted based on the application of the Certificate of Medical Benefit between 2003 and 2007, we conducted a retrospective epidemiological and prognostic analysis.

Measurements and Main Results: The prevalence and cumulative incidence of IPF was 10.0 and 2.23 per 100,000 population, respectively, with 72.7% predominance of males and an increase in frequency with age. The median survival time was 35 months, and the most common (40%) cause of death was acute exacerbation. The most important factor influencing IPF prognosis was the percent vital capacity.

Conclusions: The status of IPF in the Japanese population was clarified for the first time through our study. Our results showed that in men, the incidence of death due to acute exacerbation was higher and that due to cardiovascular disease was lower in Japan than in Western countries. These results may suggest ethnic differences in IPF.