Psoriasis is a common, chronic, inflammatory, multisystem disease with predominantly skin and joint manifestations affecting approximately 2% of the population. In this fifth of 6 sections of the guidelines of care for psoriasis, we discuss the use of ultraviolet (UV) light therapy for the treatment of patients with psoriasis. Treatment should be tailored to meet individual patients' needs. We will discuss in detail the efficacy and safety as well as offer recommendations for the use of phototherapy, including narrowband and broadband UVB and photochemotherapy using psoralen plus UVA, alone and in combination with topical and systemic agents. We will also discuss the available data for the use of the excimer laser in the targeted treatment of psoriasis. Finally, where available, we will summarize the available data that compare the safety and efficacy of the different forms of UV light therapy. © 2009 American Academy of Dermatology, Inc.