The spectrum of 182 hospital Mycoplasma pneumoniae infections, collected over a five-year period, is reviewed. The diagnosis was based on complement fixation test. Mycoplasma infection was encountered mainly in young people, mean age 29 years. Eighty-four per cent presented with an atypical pneumonia, 33 per cent had extrapulmonary manifestations mainly neurological and cutaneous. Acute respiratory failure occurred in 32 cases. Only 5 patients died. Macrolides or tetracyclines remain the most effective antibiotics but spontaneous recovery is usual.