From 1982 to 1991, we experienced 76 patients with Mycoplasma pneumoniae pneumonia which were confirmed by serologic tests. There were 32 (42%) male and 44 (58%) female patients. One patient had underlying disease of diabetes mellitus while the other patients were in good health. The age ranged from 9 months old to 72 years old. All the patients complained of fever and coughing; 63% had dry cough and 37% had sputum production. Upper respiratory tract complaints such as rhinorrhea, sore throat, or earache were noted in 57% of the patients. Fifty-five percent of the patients had GI symptoms of anorexia, nausea, vomiting, or diarrhea. Other complaints included myalgia/arthralgia (29%), headache (30%), and general malaise (32%). Dyspnea (17%) and chest pain (20%) were occasional complaints. Seventy-one percent of the patients had WBC counts < 10000/cu mm and 29% > 10000/cu mm. The mean value of C-reactive protein (CRP) was 53.1 micrograms/ml, while 16% of the patients had a CRP value above 100 micrograms/ml. Thirty-one percent of the patients were noted to have a transient elevation of serum transaminase. Four different patterns of infiltration were seen in chest radiographic manifestation: 1) peribronchial and perivascular interstitial infiltrates (18.4%), 2) nonhomogeneous patchy consolidations (22.4%), 3) homogeneous acinar consolidations (27.6%), and 4) mixed interstitial and alveolar infiltrates (27.6%). Interstitial infiltration was more commonly seen in pediatric than adult patients (46% vs 20%). Other features of the radiologic manifestation were as follows: unilateral lesions in 80% of patients, single lobe lesions in 77%, lower lobe predominant in 69%, pleural effusion in 7%, and radiographic deterioration in 10%. Mycoplasmal pneumonia should be considered in the differential diagnosis of community-acquired pneumonias.