Narrow-band ultraviolet B phototherapy with Philips TL-01 lamps is being used increasingly in the treatment of psoriasis. However, the effectiveness of phototherapy with narrow-band ultraviolet B in different clinical types of psoriasis vulgaris has not yet been evaluated in the literature. In the present study, we aimed to determine the efficacy and safety of narrow-band ultraviolet B therapy for different clinical forms of psoriasis vulgaris in our patient population. In this open study, 53 patients with psoriasis vulgaris, skin types II--IV, were enrolled. The patients were classified as guttate, nummular, plaque, or mixed according to their predominant morphological lesions. Evaluation of therapeutic efficacy was performed by comparing their Psoriasis Area and Severity Index (PASI) scores before and after treatment. The cumulative dose and the number of treatments were also calculated. Side effects were noted during the therapy. With respect to the different types of psoriasis, reductions of the PASI were not significantly different (p>0.05). The mean cumulative dose and total sessions in the plaque-type group were greater than those in the guttate and nummular groups (p<0.01, p<0.05). Complete clearing was observed in all patients in the guttate-type group, but the result was not statistically significant (p=0.064). Side effects were reported in five (11%) patients. During the 12 months follow-up period, there were no statistically significant differences in the relapse of the disease among the psoriasis groups (p=0.317). In conclusion, we found that the efficacy of narrow-band ultraviolet B therapy in patients with psoriasis decreased as the predominant lesion size enlarged. Before considering narrow-band ultraviolet B therapy for psoriasis, assessment of lesion size may be useful. Combination therapies may be more effective than phototherapy alone if the patient has predominantly large plaques.