Introduction: The advent of biotherapies has radically changed the management of IBD. However, the use of these drugs may in some cases result in to primary non-response or a loss of secondary response. Therapeutic Drug Monitoring (TDM) is a tool that was developed to manage biotherapy as accurately as possible in these situations. Material and methods: This is a retrospective descriptive study spread over 8 years of 53 patients followed for IBD put on anti-TNF(, in whom assays of residual levels of anti-TNF and anti-drug antibodies were carried out. Results: 48 suffer from Crohn’s disease and 5 from ulcerative colitis. Of these patients, 41 were on infliximab and 12 on adalimumab. The TDM performed in front of a primary non-response in 18 patients, and a loss of secondary response in 34 patients. We found immunization in 28% of patients, underdosage in 56%, and 15% had a normal dosage. Therapeutic optimization was adopted in 52% of patients, a switch in 19%, a swap in 25% of patients, and the addition of an immunosuppressant in 6.5%. The evolution was marked by the achievement of a prolonged remission in 69% of these patients. Conclusion: Pharmacological dosage of the residual rate of the anti-TNF and anti-drug antibodies currently constitutes an important element for managing the primary non-response or the loss of secondary response to anti-TNF in patients with IBD treated by biotherapy.