Etanercept, a soluble receptor antagonist to tumor necrosis factor (TNF), has been demonstrated to be effective in treating moderate to severe plaque psoriasis. It inactivates and downregulates the inflammatory and immune response induced by TNF but therefore could also reduce the host defense against malignant neoplasms.1 We report the case of a patient with preexisting undiagnosed mycosis fungoides (MF) who experienced a serious deterioration of his condition while being treated with etanercept.