Moderate-to-severe plaque psoriasis is associated with a considerable disease burden and treatment needs are often unmet. Several conventional systemic drugs are available as treatments, including methotrexate, ciclosporin, retinoids and psoralen ultraviolet A, which, although effective, are associated with considerable toxicity that limits their long-term use. Recent developments in more targeted therapies involving biological agents, such as anti-T-cell agents and inhibitors of tumour necrosis factor-alpha, offer an alternative treatment approach with the possibility of longer continuous therapy, which may translate into disease control and improved quality of life. Although the majority of data supporting the use of biological agents have been obtained in short-term studies of 3–6 months’ duration, some agents have been evaluated for longer periods of continuous administration. Comparison of efficacy among these agents may better define their role as long-term therapy. This article discusses the data currently available on both conventional and biological systemic therapies for psoriasis, in terms of short-term and long-term use.