Abstract Background The relationship between sinusitis and inflammatory bowel disease (IBD) has not yet been established. Though the two are characterised by dysfunction of the epithelial barrier, there lacks evidence on the relative contributions of infection or inflammation to this co-morbidity in IBD patients. Previous analyses from our group identified an increased prevalence of sinusitis among patients with IBD, predictive factors of developing sinusitis in IBD, and differences in stratifying patients with IBD and sinusitis (IBD+S) based on order in which these conditions were diagnosed. We now report on the factors associated with the development of IBD in patients with sinusitis. Methods This is a retrospective study at our tertiary IBD center. We utilised our institution’s electronic medical record data warehouse of 2.4 million patients to identify those with diagnostic codes for both sinusitis (J32) and IBD (K50.90 and K51.90). Patients with a confirmed diagnosis of IBD and/or sinusitis between 1/2000–5/2019 and age ≥18 years were included. Demographic and disease-related information were collected. Categorical variables were analysed using Fisher’s exact test and continuous variables were analysed using Wilcoxon rank-sum test. Results Of 14,366 patients with IBD, 386 (2.69%) patients have IBD+S. Of the 386 IBD+S patients, 118 patients (30.6%) were diagnosed with sinusitis before IBD. These 118 IBD+S patients were included in univariate and multivariate analysis with 14,753 non-IBD patients with sinusitis. The average age at IBD diagnosis among all IBD patients was 37.32 ± 18.79 years, and the average age at sinusitis diagnosis for sinusitis patients was 40.93 ± 21.42 years. On multivariate analysis, age of sinusitis diagnosis >40 years old (OR 1.52, 95% CI 1.04–2.28), black race (OR 2.82, 95% CI 1.29–7.43), white race (OR 4.33, 95% CI 2.02–11.23), and female sex (OR 1.52, 95% CI 1.03–2.28) were significant predictors of IBD in sinusitis patients (Table 1A). In comparison, multivariate analysis showed that black race (OR 8.09, 95% CI 4.91–14.26), white race (OR 3.35, 95% CI 2.08–5.80), female sex (OR 1.51, 95% CI 1.22–1.87), and bowel obstruction (OR 2.00, 95% CI 1.53–2.58) were significantly associated with sinusitis in IBD patients (Table 1B). Conclusion Sinusitis patients diagnosed older than 40 years old have 1.5 greater odds of subsequent IBD, suggesting that a diagnosis of sinusitis should prompt consideration of co-existing or subsequent IBD risk. Female sex and race are shared factors in the risk of sinusitis in IBD patients and risk of IBD in sinusitis patients.