A method of treating psoriatic arthritis in a patient by administering an IL-23 specific antibody, e.g., guselkumab, in a clinically proven safe and clinically proven effective amount and the patient achieves significant ACR20/50/70, PASI70/90/100, MDA, HAQ-DI, SF-36 PCS, MCS, LEI/dactylitis, PASDAS, GRACE, mCPDAI, DAPSA or RAPID3 improvement as measured 16, 24, 32, 40 and 48 weeks after initial treatment.