Infectious mononucleosis is usually an acute, transiently incapacitating condition, but for some sufferers it precipitates chronic illness. It is unclear which patients are at risk of a prolonged state of illness following onset of infectious mononucleosis and if there are any useful preventive measures that would facilitate recovery. The aim of this study was to review all cohort studies and intervention trials that provide information on: (a) the longitudinal course of ill health subsequent to the onset of infectious mononucleosis; (b) the relationship between psychosocial and clinical factors and recovery rate; and (c) the effect of interventions on recovery. A systematic review was conducted, based on a search of the PSYCHINFO, MEDLINE, EMBASE and CINHAL databases up to October 2001, and ISI Science and Social Sciences Citation Indices up to 22 November 2001. Eight papers were identified that gave data on illness following onset of infectious mononucleosis. The best evidence concluded that there is a distinct fatigue syndrome after infectious mononucleosis. Eight papers explored risk factors for prolonged illness following acute infectious mononucleosis. Results varied on the association of acute illness characteristics and psychological features with prolonged ill health. Poor physical functioning, namely lengthy convalescence and being less fit or active, consistently predicted chronic ill health. Three trials reported on interventions that aimed to shorten the time taken to resolve symptoms after uncomplicated infectious mononucleosis. None of the drug trials found any evidence that drug therapy shortens recovery time. The trial that compared the effect of activity with imposed bed rest, found that those patients allowed out of bed as soon as they felt able reported a quicker recovery. More information is needed on the course of ill health subsequent to the onset of infectious mononucleosis. Certain risk factors associated with delay may be amenable to a simple intervention in primary care.