We review the epidemiology of chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) and the role of infectious agents, emphasizing critical data necessary to define current research issues. The epidemiologic literature is limited, but the worldwide prevalence appears to be in the range of 2% to 10%, indicating that CP/CPPS represents an important international health problem. Recent molecular studies have documented bacterial DNA sequences in prostate tissue from CP/CPPS patients. These data suggest that colonization and/or infection occurs in the prostates of many patients with CP/CPPS. Further molecular research is needed to define the role of bacteria in the etiology of CP/CPPS.