Introduction Anaemia is the most common extraintestinal manifestation of inflammatory bowel disease, which has a negative impact on quality of life. Aim To determinate the prevalence, risk factors, and aetiology of anaemia in newly diagnosed patients with inflammatory bowel disease (IBD). Material and methods: We included 136 newly diagnosed patients with IBD. We analysed patient age, sex, laboratory tests, endoscopic and radiological examination, length of stay, and the course of hospitalisation. Results Anaemia at the time of IBD diagnosis was detected in 89 (65.4%) patients: 51 (57.3%) patients with ulcerative colitis vs. 38 (42.7%) patients with Crohn’s disease; p = 0.052. Female patients were more frequently anaemic than male patients (59.6% vs. 40.4%; p = 0.001). Anaemia was more often diagnosed in Crohn’s disease patients with ileocolonic involvement compared to other types of disease location (70.96% vs. 56.52%, respectively; p = 0.03). The prevalence of anaemia at the time of diagnosis for ulcerative colitis patients increased with disease extension: for extensive colitis anaemia was diagnosed in 64.71% compared to 35.29% in limited extension ( p < 0.05). Anaemic patients were hospitalised for significantly longer than patients with no anaemia (7.95 ±3.8 days vs. 5.88 ±2.7 days for Crohn’s disease; p = 0.02 and 9.02 ±5.0 days vs. 5.00 ±2.4 days for ulcerative colitis; p < 0.05). Conclusions Anaemia represents a frequent complication of IBD not only during the long-term course of the disease, but also at the moment of diagnosis. Anaemia is one of the factors extending the time of hospitalisation. Female sex and disease extent are strong determinant factors connected with anaemia.