Background: Today most patients with congenital heart disease (CHD) can be expected to survive into adulthood. Reports regarding the number of adults with CHD in Japan are scarce. Our study aims to define the number of these adults. Material and methods: The estimated number of infants born in Japan with major CHDs since 1947 was calculated together with mortality rates. We estimated the number of CHD survivors from data on survival rates of unoperated and postoperative patients. The number of deaths from 1968 to 1997 was analyzed using individual death certificates held by the Japanese Government. Results: In 1967, 163,058 patients with CHD including 53,846 adults were assumed to be alive. From 1968 to 1997, 548,360 patients with CHD were born and 82,919 died. A total of 622,800 patients, including 304,474 children (49%) and 318,326 adults (51%) were estimated to be alive in 1997. From 1997 to 2007, there has been an estimated increase of 9000 adults every year, and in 2007, 409,101 adults are estimated to be alive. Conclusions: The prevalence in adults with CHD in Japan has explosively increased from 1967 to 2007. There were 409,101 adults with CHD in 2007 with an annual increase of 9000. These data are crucial for planning the establishment in Japan of special facilities and resources necessary for the care of these patients. © 2009 Elsevier Ireland Ltd.