Background: Previous research has produced conflicting findings concerning whether birthdays are associated with an increased risk of suicide. This study examined the association in Tokyo, Japan. Methods: Suicide data (ICD-10 codes X60-X84) for the period 2001-2010 were obtained from the Japanese Ministry of Health, Labour and Welfare. A time-stratified case-crossover design was used with conditional logistic regression analysis being performed to estimate within-subject birthday exposures' while controlling for meteorological conditions and public holidays. Results: There were 27,007 suicides in the study period. For males the 5 days before the birthday and the week after the birthday were associated with significantly higher odds for suicide with the odds ratio being highest on the actual birthday (OR =1.677, 95% CI: 1.294, 2.172). For females, significantly higher odds for completed suicide were observed 7-11 days before the birthday. Stratified analyses showed different at risk time patterns among men from different age groups, and that married men had higher odds for suicide on, and for the 4 days before and in the 2 weeks after their birthday. Limitations: We lacked detailed information on suicides which would have enabled a better understanding of the observed associations. Conclusions: Birthdays are associated with an increased risk for suicide in Tokyo, Japan. Health professionals who work with individuals at risk of suicide should be made aware that birthdays are associated with an elevated suicide risk. This information should also be communicated in wider suicide prevention campaigns.