Ultraviolet B (UVB) phototherapy is effective for widespread psoriasis either alone or in combination with a variety of topical agents or on a rotational basis with other therapies. Significant improvement or clearing is usually accomplished with three-times-weekly to daily treatments over a period of 1 to 2 months or more. Although less complicated than systemic PUVA, administration of UVB phototherapy requires knowledge of dosimetry, potential side effects, risk factors of phototoxicity, and treatment precautions in order to minimize the risk of adverse side effects. For severe or recalcitrant psoriasis, UVB may be combined with PUVA or other systemic agents such as methotrexate or etretinate.