The findings from the UK and Canada have been suggestive, but no similar studies have yet been undertaken with Asian populations. The rise in average maternal age has also been observed in East Asian countries such as Japan and Korea, but social and cultural context differs greatly from Western countries [3, 10]. Therefore, we sought to examine the association between maternal age and children’s general health outcomes in Japan using the nationwide Longitudinal Survey of Babies in 21st Century. Based on the UK study findings, we hypothesized that older maternal age is associated with better child health.