The irritable bowel syndrome (IBS) is a very frequent cause of medical consultations in our environment, and national studies on its prevalence and associated factors are rare. Objective: To investigate the prevalence of IBS in adolescents in the city of Palmas, Tocantins, with the Rome III diagnostic criteria and its related factors. Methods: Cross-sectional study. Sample calculated for a power of 80% and alpha p 0.05. Five hundred and forty-six adolescents aged 13-19 years completed a questionnaire containing Rome III criteria for paediatric IBS, in addition to demographic data, questions about haematozia, fever, clocking, weight loss and anorexia, triggering of pain with feeding, breastfeeding, separation from parents. The schools were randomly allocated according to their location in the 3 regions of Palmas city. Subjects fulfilling Rome III criteria without any of the alarm signs mentioned were considered IBS.