Narrowband UVB (NB-UVB) has been shown to be effective for the treatment of early mycosis fungoides (MF) in light-skinned patients, but the effect of NB-UVB on patients with darker skin phototypes needs further investigation. The aim of this study was to evaluate the effect of NB-UVB in the treatment of early-stage MF in Iranian patients. In this retrospective study, 24 patients with the diagnosis of early MF (9 stage AI, 15 stage IB) were enrolled. All patients were treated with NB-UVB phototherapy 2-3 times weekly. After achieving complete response, a maintenance treatment was recommended. The response rate, side effects, and recurrence rate in the follow-up period were assessed. The follow-up period was ranged 6 to 24 months. Ten patients (41.7%) had complete remission after a mean number of 42.9 treatment and mean cumulative dose of 58.11 J/cm 2 . Twelve patients (50%) had partial response, and 2 patients (8.3%) had no response. After discontinuation of maintenance treatment, 4 of 10 patients (40%) with complete remission relapsed within a mean of 5 months. Side effects were limited to erythema (12.5%) and hyperpigmentation (4%). NB-UVB is a safe and effective method for the treatment of early MF, but it seems that more treatment sessions and higher doses of NB-UVB are required for darker skin phototypes., (© 2022. The Author(s), under exclusive licence to Springer-Verlag London Ltd., part of Springer Nature.)