Secukinumab, an interleukin (IL)-17A antagonist, was associated with disease exacerbations in Crohn's disease, and de novo cases of inflammatory bowel disease (IBD) have been reported in studies of rheumatoid diseases. However, there has been no detailed report demonstrating the linkage between secukinumab therapy and newonset IBD. We present a unique case of rapid-onset fulminant colitis after receiving 1 dose of secukinumab infusion followed by improvement with combination antibiotics, corticosteroids, and calcineurin inhibition. Health care providers should be aware of the possible association between IL-17 antagonist therapy and the risk of developing new-onset fulminant IBD.