To study the prevalence and risk factors of functional bowel disorders (FBD) in Iranian community using Rome III criteria.This study was a cross-sectional household survey conducted from May 2006 to December 2007 in Tehran province, Iran, including 18,180 participants who were selected randomly and interviewed face-to-face by a validated questionnaire based on Rome III criteria.In all, 1.1% met the Rome III criteria for irritable bowel syndrome (IBS), 2.4% for functional constipation (FC), and 10.9% of the participants had any type of FBD. Among participants with functional dyspepsia, 83.8% had FBD; the majority cases were unspecified functional bowel disorder (U-FBD). Of the subjects fulfilling the IBS criteria, IBS with constipation (52%) was the most frequent subtype. In the multivariate analysis, women had a higher risk of any FBDs than men, except for functional diarrhea (FD). The prevalence of FBD, FC and FD increased and IBS decreased with increasing age. Marital status was only associated with a decrease in the risk of FBD and FD, respectively. IBS subtypes compared with FC and FD. There was no significant difference between FC and IBS with constipation (IBS-C), except for self-reported constipation; while, IBS with diarrhea (IBS-D) had more symptoms than FD.This study revealed a low rate of FBDs among the urban population of Tehran province. The ROME III criteria itself, and the problems with interpretation of the data collection tool may have contributed in underestimating the prevalence of FBD. In addition the reliability of recall over 6 months in Rome III criteria is questionable for our population.