Seasonal variations in the incidence of gonorrhoea were observed in the 1970's with a peak in the third quarter of the year and a trough in the first and fourth quarters. The aim of this study was to determine what, if any, seasonal trends were present in Scotland and Lothian between 1984 and 1989 and postulate mechanisms to explain our observations. We observed a change in the previously reported pattern with regular peaks of infection in the first and third quarters of the year for Scotland but no regular trend in the Lothian region. The most likely explanation for the observed trends are changes in sexual behaviour related to summer vacations and seasonal work patterns but other unidentified factors probably also contribute.