BACKGROUND: Infection with Epstein-Barr virus (EBV) is almost ubiquitous in humans and generally occurs at two ages: infantile, which is usually asymptomatic and associated with poorer socioeconomic conditions, and adolescent, which causes infectious mononucleosis (IM) in ~25% cases. The determinants of whether the infection causes IM remain uncertain. We aimed to evaluate seasonality and temporal trends in IM.METHODS: Data from all Monospot tests, used as a marker for IM, were collected from the Grampian population over 16 years.RESULTS: Positive Monospot test results peaked at 17 years in females and 19 in males.