BACKGROUND: Infectious mononucleosis (IM) is common among university students. We undertook to analyze the clinical features and sequelae of the disease in a cohort of students at Edinburgh University. METHODS: Consecutive IM case patients were recruited from 2000 through 2002 at the University Health Service after diagnosis of IM. RESULTS: IM resulted in marked reductions in student study time, physical exercise, and non-exercise-related social activities, and sustained increases in reported number of hours of sleep. The disease profile differed between the sexes, with significantly more females reporting fatigue, which was more likely to be prolonged (P = .003) and to lead to loss of study time (P = .013). Female case patients were more likely to discontinue their studies following IM (16% vs 0%; P = .056). Within the typically elevated lymphocyte counts in IM, we identified an elevated gammadelta T cell component that may contribute to the disease pathogenesis. CONCLUSIONS: IM results in substantial morbidity among university students, reported as more profound in females, and affecting academic studies, physical exercise, and social activities. Immunization to prevent IM and strategies to reduce post-IM disability would be beneficial in this population.