Infection with the opportunist fungusPneumocystis cariniiremains a significant cause of morbidity and mortality in non-HIV-infected individuals immunosuppressed by a wide range of malignancies, transplantation and inflammatory conditions. Glucocorticoid use appears to be an independent risk factor for the development ofPneumocystis cariniipneumonia. Transmission from infected to susceptible patients may occur, albeit infrequently. A diagnosis ofPneumocystis cariniipneumonia may be achieved in the majority of cases by DNA detection using polymerase chain reaction on oropharyngeal mouth washes.