Iron deficiency (ID) is a frequent condition in patients with inflammatory bowel disease (IBD).Our aim was to investigate the prevalence of ID in patients with IBD.This was a prospective multicenter cross-sectional study conducted in 21 gastroenterology departments in France between January and March 2020. All adult patients with confirmed IBD who were admitted to the hospital were eligible for inclusion. ID was defined as ferritinemia ≤ 100 μg/L in patients with signs of inflammation (C-reactive protein (CRP) ≥ 5 mg/L) or ferritinemia < 30 μg/L in the absence of inflammation.In total, 1036 IBD (685 Crohn's disease and 351 ulcerative colitis) patients (52.1% women) with a mean age of 41.8 ± 15.5 years were recruited. Approximately half of the patients (504, 51.1%) were in disease remission at the time of enrollment. Systematic monitoring of iron status was performed in 12/21 (57%) participating centers, including measurements of ferritin (12/12, 100%), hemoglobin (11/12, 92%), transferrin saturation (TSAT) (6/12, 50.0%), and serum iron (5/12, 42%). About one-fifth of the patients had been treated with intravenous iron (218, 21.0%), whereas only a small percentage received oral iron (36, 3.5%). ID occurred in 97 patients (23.7% CI 95% 19.8-28.1). Patients with moderate/severe IBD activity (OR: 3.66; CI 95% 24.4-61.2; p = 0.007) or concomitant anemia (OR: 3.66; CI 95% 1.97-6.78; p < 0.001) had an increased likelihood of having ID.Patients with moderate/severe IBD activity or concomitant anemia are at increased risk of ID. Early detection and management of ID in patients with IBD is recommended.