Anti-INF-alpha therapies are used in the treatment of different inflammatory conditions, such as inflammatory bowel disease (IBD). However, paradoxical effects may occur during treatment. In other words, these drugs can induce or unmask diseases similar to those they were intended to treat. Etanercept is the main anti-INF-alpha agent associated with the development of paradoxical IBD; this drug, moreover, has no proven usefulness in the treatment of the disease. This association, which is not coincidental and meets the criteria for a temporal causal association, is infrequent and is seen particularly in patients with spondyloarthritis. Restarting treatment with etanercept may induce new intestinal symptoms. There are no endoscopic, histopathologic or clinical differences between primary and secondary IBD, and both are diagnosed in the same way. The most frequent presentation is Crohn disease. When a paradoxical event occurs, etanercept is usually replaced with infliximab, which has not been associated with disease recurrence. (C) 2016 Elsevier Espana, S.L.U., AEEH y AEG. All rights reserved.