Narbutt J, Krzyścin J, Sobolewski P, et al. - Nowadays, conventional immunosuppressants or new biological agents are used to treat patients with moderate-to-severe psoriasis. Patients in whom topical therapy is insufficient, phototherapy is used at the first-line treatment. Despite numerous studies, difficulty remains in predicting the outcome of phototherapy in individual patients. In this study, patients were asked to fill out a questionnaire about personal life and health status prior to providing standard narrow band (NB) ultraviolet B (UVB) phototherapy. Further, they underwent several standard blood tests, including selected cytokine levels, before and after a course of 20 NB-UVB treatments. Enrollment of a total of 82 participants with moderate-to-severe psoriasis was done. Prior to initiation of phototherapy, the random forest (RF) classification tool led to identification of the patients with expected good outcome from the phototherapy, shorter remission, and quitting a possible second course of the NB-UVB treatment with sensitivity over 84%, and accuracy of 75%, 85%, and 79%, respectively. Overall this approach may aid in making clinical decisions by recognizing psoriatic patients in whom phototherapy will significantly improve their skin, or those in whom other therapies should be recommended beforehand.