Anti-TNF treatment (infliximab (IFX), adalimumab (ADA)) has become standard therapy for refractory pediatric and adult Crohn's disease (CD) patients, and is used for the induction (primary response) and maintenance of remission. When effective, clinical and endoscopic remission is reached within weeks. However, primary non-response is observed in 20% of pediatric patients, and in 40% of adult CD patients, suggesting a more robust acute response to anti-TNF therapy in children as compared to adults.During maintenance treatment, 60 - 80% of patients have secondary loss of response, necessitating dose adjustments to maintain clinical response. Anti-TNF treatment is also increasingly used in ulcerative colitis (UC), and has been shown to induce remission in active disease. For UC, the comparison between the efficacy in children versus adults is more difficult to report as studies in children are scarce. Anti-TNF treatment is associated with rare but potentially fatal side effects, infusion reactions, and is an expensive treatment. To avoid overtreatment it is necessary to early identify non-responders to treatment, and therefore it is important to develop predictive biomarkers of treatment response.