Psoriasis is considered as a T-cell-mediated inflammatory skin disease which is characterized by hyperproliferation and poor differentiation of epidermal keratinocytes. While susceptibility to psoriasis is inherited, the disease is influenced by environmental factors such as infections and stress. Diet has been suggested to play a role in the aetiology and pathogenesis of psoriasis. Fasting periods, low-energy diets and vegetarian diets improved psoriasis symptoms in some studies, and diets rich in n-3 polyunsaturated fatty acids from fish oil also showed beneficial effects. All these diets modify the polyunsaturated fatty acid metabolism and influence the eicosanoid profile, so that inflammatory processes are suppressed. Some patients with psoriasis show an elevated sensitivity to gluten. In patients with IgA and/or IgG antigliadin antibodies the symptoms have been shown to improve on a gluten-free diet. The active form of vitamin D, 1,25-dihydroxyvitamin D3, exhibits antiproliferative and immunoregulatory effects via the vitamin D receptor, and thus is successfully used in the topical treatment of psoriasis. In this review, dietary factors which play a role in psoriasis are assessed and their potential benefit is evaluated. Furthermore, the risk of drug–nutrient interactions in psoriasis therapy is discussed.