Studies in adults show that pretreatment with an optimal emollient may improve transmission of ultraviolet-B. In our study, we evaluated whether the preirradiation use of mineral oil enhanced the efficacy of narrow-band ultraviolet-B phototherapy in childhood psoriasis. Twenty children, aged 5 to 14 years with widespread, symmetrical psoriasis involving >20% body surface area were enrolled in a prospective, single-blind, controlled study. Mineral oil was applied prior to irradiation over one half of the body and the other half was emollient-free control. Narrow-band ultraviolet-B phototherapy was administered to whole body twice a week on nonconsecutive days with initial dose of 50 mJ/cm(2) and increment of 10% at each session. Clinical response was evaluated as grades of erythema, scaling and induration, area of involvement and modified psoriasis area severity index score on each side at baseline, 3, 6, 9, and 12 weeks. Two patients dropped out, 18 patients completed the study. Significantly greater improvement (p < 0.05) in scaling, induration, area of involvement, and modified psoriasis area severity index score was seen on the mineral oil pretreated side as early as 3 weeks and was maintained throughout the study. Difference in erythema was noticed later at 6 weeks. The cumulative dose for clearance was significantly lower on the emollient pretreated side. No adverse effects were observed with mineral oil or narrow-band ultraviolet-B phototherapy. We conclude that preirradiation use of mineral oil enhances the therapeutic efficacy of narrow-band ultraviolet-B phototherapy in children with widespread psoriasis.