BACKGROUND: Narrowband (NB) UV-B is known as an effective and safe treatment for atopic dermatitis (AD). However, there is a lack of studies regarding prognostic factors for favorable response and its duration. OBJECTIVE: The aim of the study was to evaluate the efficacy of NB-UV-B for AD, in a large cohort and "real-life" setting. METHODS: This is a retrospective cohort study based on the medical records of patients with moderate to severe AD treated with NB-UV-B therapy between 2000 and 2017 with a long-term follow-up (≥3 years) after completing therapy. RESULTS: A total of 390 of 555 AD patients who were scheduled for NB-UV-B were included; among them, 55.4% responded well to treatment. Facial involvement, presence of adverse effects, lower number of treatments, and pretreatment immunoglobulin E levels greater than 4000 were related to poorer response. There was an overall median response duration of 12 months with a greater relapse rate among the patients younger than 18 years. CONCLUSIONS: Narrowband UV-B phototherapy shows high and long-lasting efficacy in AD. Patients with facial involvement and patients with high immunoglobulin E levels respond less to treatment. Response duration seems to be shorter for patients younger than 18 years.