Fatigue is commonly reported by patients with inflammatory bowel disease (IBD), but the determinants of IBD-related fatigue have yet to be determined. To identify the factors associated with fatigue in a large population of patients with IBD. Fatigue and nine other IBD-related disability dimensions were assessed in a cohort of 1704 consecutive patients with IBD using the IBD-disk questionnaire in a cross-sectional survey of 42 French and Belgian centers. Fatigue and severe fatigue were defined as energy subscores >5 and >7, respectively. Determinants of fatigue were assessed using univariate and multivariate analyses (odds ratios (ORs) are provided with 95% confidence intervals). The prevalence rates of fatigue and severe fatigue were 54.1% and 37.1%, respectively. Both fatigue and severe fatigue were significantly higher in patients with active disease than in patients with inactive disease (64.9% vs. 44.7% and 47.4% vs. 28.6%, respectively; p<0.001 for both comparisons). In the multivariate analysis stratified by age, sex, type of IBD and IBD activity, fatigue was associated with age >40 years (OR=0.71 [0.54-0.93]), female sex (OR=1.48 [1.13-1.93]), IBD-related sick leave (OR=1.61 (1.19-2.16]), and joint pain (OR=1.60 [1.17-2.18]), abdominal pain (OR=1.78 [1.29-2.45]), regulating defecation (OR=1.67 [1.20-2.32]), education and work (OR=1.96 [1.40-2.75]), body image (OR=1.38 [1.02-1.86]), sleep (OR=3.60 [2.66-4.88]) and emotions (OR=3.60 [2.66-4.88]) subscores > 5. Determinants of fatigue are not restricted to IBD-related factors but also include social factors, sleep, and emotional disturbances, thus supporting a holistic approach to IBD patient care.