Background: Narrowband ultraviolet B (UVB) provides complete response (CR) in 54-91% of early mycosis fungoides (MF) patients. Data concerning relapse rate and relapse-free interval after discontinuation of therapy need clarification. The purpose of this study was to evaluate the relapse rate and the relapse-free intervals of early MF patients after achieving complete response with narrowband UVB phototherapy. Methods: Retrospective evaluation of data, which belong to early MF patients treated with narrowband UVB phototherapy between May 2000 and July 2010, and followed-up until May 2012 in a single institution, for the occurrence of relapse and the time to relapse. Results: Of 31 patients, who were followed-up for a mean of 56.5 +/- 30.2 months (median 55 months, range 20-120 months), relapse was observed in 11 (35.5%) patients, within a mean of 28.8 +/- 18.2 months (median 33 months, range 4-59 months), whereas 20 (64.5%) patients stayed relapse-free for a mean of 54.2 +/- 28.8 months (median 55.5 months, range 20-119 months). Patients received maintenance phototherapy with a median duration of 12 months (range 1-30 months) after achieving complete response. Conclusion: Results indicate that narrowband UVB phototherapy may induce low relapse rates and long relapse-free intervals for early MF.