Psoriasis is a common inflammatory skin condition with high morbidity. Unfortunately, the etiology of the disease currently is unknown, although genetic and environmental factors appear to play important roles in its pathogenesis. Because lasers are used extensively in dermatology to treat various conditions with proven efficacy and safety, they have been investigated as alternatives for treating psoriasis due to side effects that can occur with long-term use of potent topical corticosteroids. Lasers also have the potential to target specific plaques. Modalities that have been investigated for treatment of various forms of psoriasis include the 308-nm excimer laser, psoralen plus UVA (PUVA), narrow-band UVB (NB-UVB), the pulsed dye laser, the 1064-nm Nd:YAG laser, the CO2 laser, and photodynamic therapy. In part 1 of this series, we review the etiology and clinical features of psoriasis and evaluate the efficacy and safety of the 308-nm excimer laser, PUVA, and NB-UVB in the treatment of this common disease.