Cytomegalovirus mononucleosis: risk for fathers of young children.

A case of pyrexia of unknown origin in a 35-year-old man, who had become a father nine months earlier, is presented. A diagnosis of cytomegalovirus mononucleosis was achieved only after extensive investigations. It is suggested that cytomegalovirus mononucleosis should be added to the differential diagnosis when investigating pyrexia of unknown origin in fathers of young children.