BACKGROUND & AIMS: Data on safety and long-term follow-up evaluation of population-based cohorts of inflammatory bowel disease (IBD) patients treated with infliximab are sparse. The aim of this article is to describe the use of infliximab in a national Danish population-based IBD cohort during 1999-2005. METHODS: Medical records of all infliximab-treated IBD patients were scrutinized to abstract information on patient demographics, treatment efficacy, and adverse events. RESULTS: A total of 651 patients (619 with Crohn's disease, 15 with ulcerative colitis, and 17 with colonic IBD type unclassified) received infliximab during 1999-2005. A total of 3351 infusions were administered, with a median of 3 infusions per patient. A positive clinical response was observed in 82.7% (95% confidence interval, 79.9-85.5) of patients. Infusion reactions were observed after 146 of 3351 infusions (4.4%). Significantly fewer infusion reactions were seen in patients also receiving azathioprine or methotrexate (63 of 2079; 3.0%), compared with patients not receiving azathioprine or methotrexate (83 of 1272; 6.5%) (P < .0001). Severe adverse events were observed after 112 of 3351 infusions (3.3%) in a total of 95 patients (14.6%). Four patients developed cancer versus 5.9 expected (standardized incidence ratio, 0.7; 95 confidence interval, 0.2-1.7) and 13 patients died versus 6.9 expected (standardized mortality ratio, 1.9; 95% confidence interval, 1.0-3.2). Two deaths caused by infections were possibly related to infliximab. CONCLUSIONS: Infliximab seemed effective in IBD and generally was well tolerated. However, rare but severe adverse events occurred, and patients receiving infliximab therefore should be selected carefully and monitored closely. No lymphomas and no increased risk of cancer were observed.