One hundred and ten patients with empyema thoracis were diagnosed at Buddhist Tz’u-Chi General Hospital between December 1986 and February 1993. 17 patients (15.5%) had sterile cultures. There were 141 microbial isolates (1.52 isolates per case) among the 93 culture-positive patients. The organism most commonly isolated was Viridans Streptococcus (28 isolates), followed by Klebsiella (16 isolates). A single pathogen was identified from 65 patients (69.9%) and more than one species (mixed infection) were found in the other 28 patients. The gram-negative rods represented the largest group (37.6%), followed by Streptococcus (27.7%), Staphylococcus (8.5%), Enterococcus (7.8%), Tubercle bacilli (7.8%) and anaerobic bacteria (6.4%). There were 13 cases of tuberculosis empyema. Empyema thoracis remains a common clinical problem in Eastern Taiwan.