This epidemiological study of irritable bowel syndrome (IBS) was the first one of the type in Croatia. The aim of the study was to determine prevalence and association between IBS and gender, age, education and urban/rural living. Study design included a questionnaire based on Rome criteria, which was send to 500 study subjects by post. Study population matched the adult population of Croatia according last census. Study result showed a high prevalence of IBS: i.e. 28% (10% of males and 18% of females). Age, education and urban/rural type of living were not related to the prevalence of IBS. Logistic regression gave gender-body mass index (BMI) model for IBS determination: the relative risk for getting IBS in females was by 165% higher than in males and BMI increase of 5 kg/m2 increased the risk of IBS by 36%. BMI was indicated as a possible new factor of IBS prevalence.