 A modified local PASI psoriasis area and severity index score adapted for the evaluation of the hands and feet will be performed by a blinded investigator at baseline and the onset of PUVA treatment, in biweekly intervals during the course of PUVA treatment, in monthly intervals after discontinuation of PUVA and in bimonthly intervals during a 1-year follow-up period. The study will be terminated in case of a significant relapse which is defined by a PASI score of 50 of the baseline score. 