Peritonitis is one of the most serious complications of continuous ambulatory peritoneal dialysis (CAPD). Approximately 20% of peritonitis infections have been reported to be resistant to initial therapy, either failing to resolve with appropriate antibiotics or relapsing within 2 weeks of antibiotic discontinuation. To investigate the current situation with regard to resistant peritonitis, we retrospectively examined the incidence and the organisms of resistant peritonitis in our unit over a period of 9 years. From January 1, 1994, to January 1, 2003, we introduced 325 patients onto CAPD. At January 1, 2003, we followed up 172 patients who were receiving CAPD in our unit. During 1994-1996, 12 cases of peritonitis and 3 cases of resistant peritonitis (25%) occurred among our patients. Microbiologic examination revealed that the organisms involved in peritonitis were alpha-streptococcus (17%), coagulase-negative staphylococcus [CNS (17%)], and methicillin-sensitive Staphylococcus aureus [MSSA (17%)]. The organisms of resistant peritonitis were methicillin-resistant S. aureus [MRSA (67%)] and methicillin-resistant CNS (33%). During 1997-1999, 39 cases of peritonitis and 13 cases of resistant peritonitis (33%) occurred among our patients. The most frequently cultured organisms in peritonitis were CNS (26%), Candida species (13%), and alpha-streptococcus (10%). The organisms of resistant peritonitis were methicillin-resistant CNS (46%) and Candida species (38%). In the most recent 3-year period (2000-2002), our patients experienced 57 cases of peritonitis and 24 cases of resistant peritonitis (42%). The organisms of peritonitis were alpha-streptococcus (46%), CNS, MSSA, Escherichia coli, and Candida species (38%). However, the organisms of resistant peritonitis were methicillin-resistant CNS (13%), Candida species (21%), Pseudomonas aeruginosa (13%), Serratia (13%), Citrobacter (13%), and Corynebacterium (13%). In the last several years, methicillin-resistant CNS has come to be main organism of resistant peritonitis. In addition, opportunistic infection has become a serious peritonitis problem. Given these data, we conclude that the incidence of resistant peritonitis is increasing and that the organisms of resistant peritonitis are changing.