Psoriatic arthritis occurs very frequently in patients with psoriasis. It is not clear whether psoriatic arthritis and psoriasis are two distinct entities or one disease. The IL-23/IL-17 axis plays a pivotal role in both conditions. Differential expression of IL-17 and IL-22 occurs at various sites and may explain arthritis and skin lesions. Biologics neutralizing IL-17A or IL-23/IL-12 are effective therapies for both disease. Psoriatic arthritis and psoriasis may be the same disease.