Although seasonal variations in births are observed in all human populations, the links between calendar events and sexual activity have received little attention in relation to health promotion and service provision. We have plotted various relevant data--routinely collected data for births within and outside of marriage, abortions, sexually transmitted infections, human immunodeficiency virus tests and condom sales figures--by calendar period. The trends point consistently to an increase in sexual activity and unsafe sex occurring at or around the Christmas period, and a longer but less pronounced subsidiary period of increased sexual activity and unsafe sex coinciding with the summer vacation. We conclude that seasonal patterns of sexual activity have implications for provision of sexual health services and for the timing and targeting of sexual health promotional interventions.