BACKGROUND: Residual pleural thickening is frequently seen following treatment for tuberculous pleurisy, and pleural decortication is performend occasionally in patients with severe residual pleural thickening. However, predictive factors for the development of residual pleural thickening are uncertain at the initial diagnosis of the tuberculous pleurisy. Therefore, the purpose of this study was to identify the associated factors for residual pleural thickening at initial diagnosis. METHODS: We separated 63 patients diagnosed as tuberculous pleurisy into two groups; group 1 consisted of patients without residual pleural thickening and group 2 comprised patients with residual pleural thickening at the end of tuberculous pleurisy treatment. We analyzed the clinical characteristics, radiological findings, pleural biopsy and characteristics of pleural fluid between group 1 and group 2. RESULTS: The study population and clinical symptoms of the two groups were not significantly different and the duration of symptoms before treatment and the peripheral WBC were similar between the two groups. The presence of pulmonary tuberculosis, pleural fluid loculation or the amount of pleural effusion sid not differ significantly between the thwo groups. The incidence of positive AFB staining(group 1 : 8%, group 2 : 38%) and granuloma(group 1 : 30%, group 2 : 62%) on pleural biopsy specimens was significantly higher in group 2 than in group 1. Pleural fluid WBC and differential count, adenosine deaminase level, pH, preotein level or glucose level did not differ between the two groups. However, group 2 had higher LDH levels (1370±208mg/dl) than group 1 (860±71mg/dl, p<0.05). CONCLUSION: In tuberculous pleurisy, patients with residual pleural thickening following treatment demonstrated a higher incidence of posivive AFB staining and granuloma on the pleural biopsy specimens or higher LDH level in the pleural fluid than patients wihtout residual pleural thickening From these results, we speculate that the amonut of tuberculous bacilli and granuloma are probably correlated with residual pleural thickening in the tuberculous pleurisy.