Background:It is believed that the incidence of cystic fibrosis (CF) among Asiatic races, including the Japanese, is very rare. This epidemiological study was carried out to investigate the incidence of CF in Japan.Methods:We collected literature describing CF cases among pure Japanese and found 124 cases reported as CF during the 43 years from 1951, when the first case was reported, to 1993. Only 104 cases (57 male and 47 female patients) of 124 cases met our diagnostic criteria.Results:A simple calculation based on the number of reported CF cases and of live births after 1980 suggested that the incidence of CF is about 1 in 350,000 in the Japanese population. Twenty-nine (27.9% of the total) of 30 patients diagnosed in the neonatal period presented symptoms of meconium ileus, an incidence higher than that reported for the white population.Conclusions:Our study results suggest that the incidence of CF in the Japanese population is even rarer than had been estimated before and that there is a genetic difference between northern European and Japanese populations.