A 52‐week postmarketing surveillance study was initiated to evaluate the safety and effectiveness of guselkumab, a human anti–interleukin 23 subunit p19 monoclonal antibody, in Japanese patients with psoriasis vulgaris, psoriatic arthritis, generalized pustular psoriasis, and erythrodermic psoriasis in real‐world practice. This evidence concerns the gene IL23A and generalized pustular psoriasis.