Psoriasis (Ps) is a chronic inflammatory disease with an important genetic component. It shares pathophysiological mechanisms with other autoimmune diseases such as psoriatic arthritis (PsA), rheumatoid arthritis (RA) and Crohn's disease (CD). These conditions can be treated using biological drugs such as infliximab, adalimumab and etanercept, which selectively block the proinflammatory cytokine tumor necrosis factor (TNF)-α. Although these agents have greatly improved the prognosis of Ps, PsA, RA and CD, they do not cure the disease and are expensive; in addition, significant proportions of patients do not respond or develop serious adverse effects. Therefore, it is important to investigate biomarkers, such as gene polymorphisms, that can predict which patients will respond best to a specific drug. Some polymorphisms in genes TNF, TNF receptor superfamily 1B (TNFR1B) and TNFα-induced protein 3 gene (TNFAIP3) have been associated with response to anti-TNF therapy in patients with Ps. The present article reviews other polymorphisms that could also play a role in prediction of response to these treatments.