Although biologics are important inflammatory bowel disease therapies, loss of response (LOR) remains problematic. We evaluated LOR to biologics in our Crohn disease (CD) patients receiving biologics. Of 137 biologic-treated CD patients, 68 continuously receiving the same biologic type for at least 1 year were divided into 2 groups: infliximab (IFX) (n = 39) and adalimumab (ADA) (n = 29). Clinical courses were compared at biologic introduction and at 1 year. Both groups were retrospectively analyzed for LOR at and beyond 1 year after biologic introduction (study endpoint). Patients were then divided into LOR and non-LOR groups to identify factors predicting LOR. At 1 year after biologic introduction, decreases in CD activity index were 94 ± 105 in the IFX and 102 ± 89 in the ADA group, not significantly different. Blood test data did not differ between these groups. LOR occurred in 14 IFX and 5 ADA group patients. Event-free rates at 5 years after biologic introduction were 62% in the IFX and 61% in the ADA group. Patients achieving clinical remission 1 year after biologic introduction accounted for 69% of the IFX and 90% of the ADA group, while respective rates of secondary LOR at 5 years were 32% and 26%. C-reactive protein (CRP) at biologic introduction (odds ratio [OR], 1.5; 95% confidence interval [CI], 1.04-2.06; P = .02) and age at CD onset (OR, 1.1; 95% CI, 1.01-1.20; P = .03) predicted LOR. As to IFX and ADA efficacies after 1 year of administration, there were no significant differences in event-free rates for the 5 years after biologic introduction or the secondary LOR rate. CRP at biologic introduction and age at CD onset predicted LOR.