The prevalence of toxigenic Clostridium difficile in Korea has been reported to be approximately 60–80 %. Although the prevalence of the tcdA−tcdB+ C. difficile strain was less then 5 % prior to the year 2000, it has become an emerging nosocomial pathogen in Korea. Therefore, we have attempted to determine the multicentre nationwide prevalence of tcdA+tcdB+ and tcdA−tcdB+ C. difficile for epidemiological purposes. C. difficile strains (n=724, 30 from 2000, 80 from 2001, 74 from 2002, 76 from 2003, 179 from 2004, 285 from 2005) were obtained retrospectively from January 2000 to December 2005 from in-patients at 6 hospitals, all of whom were suspected of having C. difficile-associated disease (CDAD), colitis or pseudomembranous colitis. The numbers of participating hospitals varied yearly (1 in 2000, 2 in 2001–2003, 3 in 2004, 5 in 2005). The hospitals were located in Seoul (n=4), Kyunggi Province (n=1) and Busan (n=1), Korea. PCR assays for tcdA and tcdB genes were conducted using 724 unduplicated C. difficile isolates. The mean prevalence of tcdA+tcdB+ and tcdA−tcdB+ C. difficile strains over the 6 years was 51.8 % (38.4–59.3 %) and 25.8 %(10–56.0 %), respectively. The mean prevalence of tcdA−tcdB+ C. difficile strains was less than 7 % until 2002, but began to increase in 2003 (13.2 %) and achieved a peak in 2004 (50.3 %). In 2005, the mean prevalence of tcdA+tcdB+ and tcdA−tcdB+ C. difficile strains was 47.7 % (30.9–60.3 %) and 27.0 % (17.6–54.8 %), respectively. This nationwide epidemiological study showed that tcdA−tcdB+ C. difficile strains have already spread extensively throughout Korea, and our results provide basic data regarding the controversies currently surrounding the toxigenicity of tcdA−tcdB+C. difficile. The use of enzyme immunoassays capable of detecting both TcdA and TcdB is strongly recommended for the diagnosis of CDAD in microbiology laboratories, in order to control the spread of the tcdA−tcdB+ strains of C. difficile.