The aim of this study was to investigate the duration of remission periods in psoriasis after narrowband ultraviolet B (NB-UVB) phototherapy, especially during multiple cycles of treatment. We analyzed 63 patients (101 cases) demonstrating marked improvement after NB-UVB phototherapy. The remission period was defined as the duration of time from the end of phototherapy until treatment using either phototherapy or systemic treatments was required again. It was found that an age of 60 years or older, history of systemic therapy within 6 months and three or more phototherapy cycles were significantly associated with shorter remission periods. Furthermore, multivariate analysis confirmed that three or more phototherapy cycles (odds ratio [OR], 4.0; 95% confidence interval [CI], 1.73-9.33; P = 0.001) and a history of systemic therapy (OR, 2.2; 95% CI, 1.27-3.95; P = 0.005) were independently associated with the shorter remission period. In conclusion, when planning NB-UVB phototherapy for psoriatic patients who have undergone multiple phototherapy cycles, clinicians should consider the possibility of shorter remission periods.