The effectiveness of methoxsalen and ultraviolet light (PUVA) in treating is reviewed. The use of this therapy, its mechanism of action, pharmacology, pharmacokinetics, adverse reactions, dosage, and comparison with other forms of therapy, are discussed. Administered orally, methoxsalen in combination with long-range ultraviolet light (UVA) is effective in treating patients with moderate to severe forms of psoriasis. Although the short-term risks associated with PUVA therapy are minimal, the long-term risks of oncogenicity have not been evaluated thoroughly. Common adverse reactions to methoxsalen and UVA are nausea, pruritus, and erythema, but usually they can be managed by minor modifications in the treatment regimen. Methoxsalen and UVA therapy should be reserved for patients with moderate to severe forms of psoriasis that do not respond to other forms of therapy until the long-term risks of oncogenicity are evaluated.