Background:Several environmental factors have been associated with onset of inflammatory bowel diseases (IBD): smoking, hygiene, microorganisms, oral contraceptive pills (OCPs), non-steroid anti-inflammatory drugs, antibiotics, appendectomy, diet, breastfeeding, vitamin D, stress and ambient air pollution. The aim of this study was to investigate the prevalence of these factors in a Romanian and Belgian population with IBD. Material and methods:A total of 129 patients with an IBD diagnosis (76 from Romania and 53 from Belgium) participated in an interview and were asked to fill in a questionnaire regarding environmental factors before and after the onset of IBD; 35 Romanian and 21 Belgian healthy individuals constituted the control group. Results:A total of 40 patients with ulcerative colitis (UC) and 89 with Crohn's disease (CD) were included. Gender distribution was 43% males and 57% females. They had a median age of 42 years (range between 19-74 years), a median disease duration of eight years and 79% were in clinical remission. Both Romanian and Belgian IBD patients reported an increased antibiotic consumption before IBD onset compared to controls: 58% vs 10% (p<0.001) and 51% vs 5% (p<0.001), respectively. Belgian IBD patients declared significantly more frequent OCP use (53% vs 9%, p <0.001), they were breastfed in a lower proportion (49% vs 76%, p <0.001) and had experienced a higher level of psychosocial stress (p<0.001). Conclusion:Antibiotic consumption before IBD onset may play a pivotal role in IBD development in both Romanian and Belgian populations. In Belgian patients, OCP consumption, a higher level of psychosocial stress and lack of breastfeeding may also be involved.