Objectives: Probing for clues to the pathogenesis of interstitial cystitis/painful bladder syndrome (IC/PBS), we sought antecedent nonbladder syndromes that distinguished incident IC/PBS cases from matched controls. Methods: Female incident IC/PBS cases were recruited nationally, and their IC/PBS onset date (index date) was established. The controls were recruited by national random digit dialing and matched to the cases by sex, age, region, and interval between the (assigned) index date and interview. The prevalence of 24 nonbladder syndromes before the index date was assessed, 7 by multiple methods. Results: The cases with IC/PBS had greater antecedent prevalence of 11 syndromes, and 243 of 313 cases (78%) vs 145 of 313 controls (45%) had multiple syndromes (P < .001). Fibromyalgia-chronic widespread pain (FM-CWP), chronic fatigue syndrome, sicca syndrome, and irritable bowel syndrome were associated with each other by pairwise and factor analyses using numerous assumptions. Cases with FM-CWP, chronic fatigue syndrome, sicca syndrome, and/or irritable bowel syndrome (n = 141, 45%) were more likely to have other syndromes (ie, migraine, chronic pelvic pain, depression, and allergy). Three other syndrome clusters were identified; each was associated with this FM-CWP cluster. Conclusions: Eleven antecedent syndromes were more often diagnosed in those with IC/PBS, and most syndromes appeared in clusters. The most prominent cluster comprised FM-CWP, chronic fatigue syndrome, sicca syndrome, and irritable bowel syndrome; most of the other syndromes and identified clusters were associated with it. Among the hypotheses generated was that some patients with IC/PBS have a systemic syndrome and not one confined to the bladder. © 2009 Elsevier Inc. All rights reserved.