A 67 year-old man was diagnosed 10 years ago with severe plaque psoriasis and was hospitalized for re-evaluation of therapy. He was treated previously with topical corticosteroids, methotrexate, and phototherapy. As part of the assessment protocol for initiation of biological treatment, a tuberculin skin test was done, which was positive without signs of active tuberculosis. Isoniazid therapy was started with marked improvement of psoriatic lesions before biologic treatment could be initiated.