PURPOSE: This study was performed to observe the epidemiological pattern of M. pneumoniae pneumonia during the period from 1993 to 2002 and also to see some clinical characteristics of M. pneumoniae pneumonia during recent five years. METHODS: We had performed a retrospective analysis of epidemiological pattern of occurrence in 682 patients with M. pneumoniae pneumonia admitted to Department of Pediatrics of Han-il General Hospital from January, 1993 to December, 2002. RESULTS: The annual ratio of M. pneumoniae pneumonia was compared with the total numbers of respiratory tract infection patients. The ratios were 19.1% in 1993, 13.0% in 1994, 5.6% in 1995, 12.8% in 1996, 18.6% in 1997, 22.6% in 1998, 1.1% in 1999, 13.3% in 2000, 9.1% in 2001, 6.0% in 2002, and 19.9% in 2003. The epidemics have occurred in 1993, 1997, 1998, 2000, and 2003 years showing 3~4 year intervals. The peak incidence of age was four to six years old(286 cases; 41.9%) and male-to-female ratio was 1 : 1.1. Monthly distribution showed a high frequency from August to December and the major outbreak occurred in November(119 cases; 17.4%), in October(106 cases; 15.5%), and in December(96 cases; 14.1%) in order of frequency. The most common symptoms were cough(660 cases; 96.8%), fever(569 cases; 83.4%), and sputum(522 cases; 76.5%) in that order. Leukocytosis was observed in 31.2% of patients based on a normal range according to the adjusted age. Increased ESR(≥20 mm/hr) was noted in 42.5% of cases and CRP was positive in 37.8% of cases. On the chest X-ray examination, pulmonary infiltration was noted in 557 cases(81.7%), and the patterns of pneumonic infiltration were bronchopneumonia(78.0%), lobar(35.5%), lobular(19.2%), and interstitial pneumonia(28.7%). Complications were paranasal sinusitis(41 cases), acute otitis media(23 cases), pleural effusion(19 cases). cervical lymphadenitis(18 cases), and glomerulonephritis(1 case). CONCLUSION: The pattern of M. pneumoniae pneumonia from 1997 to 2003 noted 3~4 year interval with peak monthly distribution of October and November compared with 3 year interval and peak incidence of summer period before 1996.