BACKGROUND: Diagnosis of subpulmonary effusion is thought to be somewhat difficut more than pulmonary effusion. Clinical course and pathophysiology are thought to be different from typical pulmonary effusion. This study was done for increasing high suspicious index and early diagnosis of subpulmonary effusion. METHOD: Among the patients at dept. of chest medicine, National Medical Center from January 1990 to Dec. 1993, 232 cases of typical pulmonary effusion and 42 cases of subpulmonary effusion were studied. RESULT: 1) The ratio of subpulmonary effusion and typical pulmonary effusion was about 1:5 2) Male to Female ratio was 1:1 in both effusion. 3) Rt. side pleural and subpleural effusion were slightly predominant. 4) Subjective symptoms are chest pain, cough and exertional dyspnea. There is no difference between subpulmonary and typical pulmonary effusion. 5) Duration of symptom was slightly longer in subpulmonary effusion. 6) The most common cases of pleural effusion is tuberculosis in both subpulmonary & typical pulmonary effusion. Non-specific pleuritis was more common in subpulmonary effusion. 7) Pleural effusion was recurred about one fifth in both subpulmonary & pulmonary effusion. CONCLUSION: We studied clinical course and laboratory findings between subpulmonary & pulmonary effusion. However there are no definite difference between subpulmonary & pulmonary effusion. Duration of symptom was slightly longer in subpulmonary effusion. Most common cause was tuberculosis. Non specific pleuritis was more prevalent in subpulmonary effusion.