Chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) is a common disorder and accounts for approximately 2 million visits to physicians annually in the United States. The substantial impact of CP/CPPS includes bothersome lower urinary tract symptoms, sexual dysfunction, reduced quality of life, and increased health care expenditures. The syndrome is diagnosed only on the basis of symptoms, principally pain or discomfort in the pelvic region. No objective measures can help define the disease. Although bacteria can infect the prostate, most men with prostatitis have a negative midstream urine culture, indicating that bacteria may not be the cause of their symptoms. Such men are classified as having National Institutes of Health (NIH) category III prostatitis, the most common of the clinically defined prostatitis syndromes. It is by no means clear that the disease is characterized by inflammation of the prostate or that the prostate is responsible for symptoms in a substantial proportion of patients. Because of this uncertainty, the term CP/CPPS is used. Chronic prostatitis/chronic pelvic pain syndrome is commonly seen by primary care practitioners, internists, and urologists. In the Olmsted County Study of Urinary Symptoms and Health Status Among Men, a population-based study in Olmstead County, Minnesota, the overall prevalence rate of a physician-assigned diagnosis of prostatitis was 9%. Population-based surveys of symptoms have estimated that the prevalence of the syndrome ranges from 9% to 12% among men. It is difficult to estimate the proportion of patients with symptoms lasting longer than 3 months whose disorder remains refractory to empirical therapy. These patients are commonly seen by urologists, but whether they represent a minor subpopulation of the overall symptomatic group or make up the majority of patients is unknown. The investigators chose to study these patients because they present with a troubling, long-standing problem and are usually treated with agents of unclear benefit. Even if a relatively large number of men whose symptoms last 3 months or more are cured by standard empirical therapy and the clinical scenario the investigators describe is uncommon, men with refractory symptoms still present a substantial problem to internists and urologists who have little information to guide therapy. Because the cause of CP/CPPS is unknown, affected men receive many empirical therapies. The 2 most common treatments prescribed by physicians are antimicrobial agents and alpha-adrenergic receptor antagonists, although there is little objective evidence to support their use. Quinolones, such as ciprofloxacin, are commonly used to treat CP/CPPS because of their excellent penetration into the prostate and broad spectrum of coverage for uropathogens and other organisms traditionally believed to be associated with the syndrome. Tamsulosin, an alpha-blocker, is an effective treatment for lower urinary tract symptoms in men with benign prostatic hyperplasia, and it has been hypothesized that tamsulosin may improve these symptoms in men with CP/CPPS. This randomized clinical trial was designed to evaluate whether ciprofloxacin or tamsulosin reduces symptoms of long-standing CP/CPPS of at least moderate severity, typical of the 488 men in our Chronic Prostatitis Cohort Study. The primary purpose of the trial was to test the most common prescription treatments given to men with CP/CPPS, who are commonly seen in our referral-based urologic practices.