Klebsiella pneumoniae has emerged as the leading liver abscess pathogen in Taiwan, with the percentage rising from 30% in the 1980s to over 80% in the 1990s. Most of the patients with K. pneumoniae liver abscess are diabetic and without biliary tract disease. Some patients develop serious extrahepatic complications such as endophthalmitis, meningitis, lung abscess, and necrotizing fasciitis. Pulsed-field gel electrophoresis (PFGE) was used for cluster analysis of 96 isolates from patients with liver abscess and 60 isolates from patients with other diseases. A total of 136 PFGE types were identified. Among the 96 liver abscess-associated isolates, 60 (62.5%) were classified in major cluster A. Cluster A included 41 PFGE types (types 1 to 41) which had a genetic similarity of at least 72.4% +/- 9.4%. The PFGE patterns of cluster A strains are so similar that they could have originated from the same ancestor. This study demonstrates that cluster A plays an important role in the high incidence of K. pneumoniae liver abscess in Taiwan.