In this randomized clinical trial, 39 patients with psoriasis vulgaris were randomized in two groups. Intervention group received narrow band ultraviolet B (NBUVB)+isotretinoin (0.5 mg/kg/day), control group received NBUVB+placebo. Psoriasis Area Severity Index (PASI) scoring was recorded at baseline and weeks 4, 10, and 14. Thirty-seven patients completed the study. According to recorded PASI scores the difference between efficacies of two treatments was not significant. Complete clearing was noticed in 14 and 13 patients in intervention group and controls. The mean cumulative NBUVB dose in intervention group and controls was 29.95 ± 16.11 vs. 45.77 ± 7.72 J/cm2 (P=0.004). Isotretinoin+NBUVB can reduce number of phototherapy sessions and cumulative NBUVB dose.