BACKGROUND: The incidence of mycoplasmal pneumonia is predominantly at childhood and early adulthood, but in adults, its incidence is low and its symptoms and physical findings are nonspecific. The definite diagnosis of M. pneumoniae pneumonia can be made by sputum culture, but requires several weeks for positive results, and the early diagnosis must initially be based on the serologic tests and appropriate clinical findings. Thus, we evaluated the clinical aspects of M. pneumoniae pneumonia in the adults patients. METHOD: Among the admitted patients due to pneumonia, the definite diagnosis is anti-M. pneumoniae antibody titer of > 1:40 and a single cold agglutinin titer of > 1:64. The presumptive diagnosis is anti-M. pneumoniae antibody titer of > 1:40 or a single cold agglutinin titer of > 1:64 and the clinical characteristics or chest X-ray findings are compatible with M. pneumoniae pneumonia. We studied the age and sex distribution, seasonal distribution, clinical symptoms, physical findings, serologic test, chest X-ray findings, treatment and its progression. RESULTS: 1) The age distribution was even and the ratio of male to female was 1:1. 2) The monthly distribution was most common in January(16.7%) and the seasonal distribution in autumn and winter(autumn: 30%, winter: 33.3%). 3) The cold agglutinin titers were higher than 1:64 in 12 cases(40%), and reached the peak level around 2 weeks from onset and antimycoplasma antibody titers were higher than 1:160 in 5 cases(16.7%). 4) On the chest X-ray, pulmonary infiltration was noted in 28 cases(93.3%) among 30 cases and right lower lobe involvement was the most common(33.3%) and both lower lobe involvement was noted in 7 cases(23.3%). 5) The mean treatment duration was most common(33.3%) in 1 week to 2 weeks after admission and 26 cases(86.7%) were improved within 4 weeks. 6) On admission, there was fever(> or =38.9degreesC) in 17 cases(56.7%), and the fever subsided in 12 cases(70%) within 3 days after treatment using erythromycin. CONCLUSION: The mycoplasmal pneumonia in adults shows milder clinical patterns than that in childhood and can be completely recovered without complication by early diagnosis and treatment.