The etiology of irritable bowel syndrome (IBS) tends to be complex and multi-factorial and there is still a lack of understanding of how different psychosocial factors are associated with the syndrome. Our aim was to examine the occurrence of psychosocial and behavioural factors among patients diagnosed with IBS in primary care. The study had an epidemiological population-based case-control design comparing 347 IBS cases to 1041 age and sex matched controls from the general population. A survey was directed to cases and controls based on validated questions asking for mood status, job strain, family history of IBS, and sleeping habits as well as education, nutritional and exercise habits and medication. In multivariate analyses, independent associations were found between IBS and lack of influence on work planning, a family history of IBS, anxiety, and sleeping disturbances. Important factors associated with IBS diagnosis among females were anxiety as well as family history of IBS and lack of co-determination at work. For males, only lack of influence on working pace and family history of IBS remained independently associated with an IBS diagnosis. The causal associations of the complex risk factor panorama for IBS warrants further study. This study indicates that there should be a special focus on investigating the psychosocial working conditions and their associations to IBS.