PURPOSE: This study was designed to document the etiologies and the characteristics of parapneumonic effusion in children. METHODS: During a 17-year period from 1987 to 2004, parapneumonic effusion was confirmed in 86 children at Gyeongsang National University Hospital. The clinical records of these children were reviewed and radiological findings and laboratory data, especially results of thoracentesis, were analyzed retrospectively. RESULTS: M. pneumoniae(34 subjects) was the most common pathogen at all over age, especially above 1-years-old. There were diagnosed with clinical characteristics and serologic tests. The 2nd most common pathogen revealed non tuberculous bacteria(14 subjects). A species of bacteria at no tuberculous bacteria revealed S. aureus(5), S. pneumoniae(3), P. aeroginosa(3), other staphylococcus (2), and K. pneumoniae(1). There were confirmed with sputum culture or pleural fluid culture or blood culture. S. aureus was most common pathogen in infants. The 3rd common pathogen was M. tuberculosis(7). There were confirmed with skin tuberculin tests and AFB stains. Another that was classified as a non bacteria was adenovirus(2). Complications of parapneumonic effusion such as pleural thickness occurred on M. tuberculosis(1). Non tuberculous bacteria, especially S. aureus revealed a serious predominance of polymorphocyte at pleural fluid, and lowest pleural pH and glucose, and highest pleural protein and LDH. Tuberculosis revealed high pleural protein and LDH. CONCLUSION: Age and chemistries of pleural fluid might be helpful in differentiating various etiologies of parapneumonic effusion. If there were suspicious of tuberculosis and non-tuberculous bacteria, more aggressive approaches were needed to prevent complication.