A method of treating psoriasis in a patient previously treated with and determined to be an inadequate responder to an IL-12/23p40 antibody by administering an IL-23 specific antibody, e.g., guselkumab, in a safe and effective amount and the patient achieves PASI75, PASI90, PASI100 or IGA 0 or 1 score as measured 16, 24, 32, 40 and 48 weeks after initial treatment.