OBJECTIVE Mycosis fungoides (MF) is the most common variant of cutaneous T-cell lymphomas primarily involving the skin. Early-stage MF is characterised by non-specific skin lesions and non-diagnostic biopsies. While skin-focused treatments, such as PUVA and narrowband UVB (nbUVB), are the most frequently recommended treatments, the UVA1 efficacy has been researched in recent years. The purpose of this study was to evaluate the clinical, histopathological and immunohistochemical aspects of UVA1 treatment in patients with early-stage MF. METHODS The modified severity weighted assessment scale (mSWAT) was used for total skin body scoring before and after treatment. Skin punch biopsies were taken from the patients before and after treatment. UVA1 therapy was performed five times each week. RESULTS This study included 26 patients with early-stage MF. The total number of UVA1 sessions varied between 15 and 34. Complete response was observed in 8 (30.8%) of 26 patients (30.8%). The median mSWAT score decreased statistically significantly from 7.1 to 2.0 after treatment (p < .001). Histopathological complete response was observed in 2 (9.5%) of 21 patients. A statistically significant decrease in dermal interstitial infiltrate was observed on histopathological examination after treatment (p = .039). Epidermal CD4/CD8 levels decreased statistically significantly higher from a median of 2.5-1.2 in the complete clinical response group after treatment (p = .043). CONCLUSIONS According to our results, UVA1 treatment has an effect on early-stage MF in terms of clinical, histopathological and immunohistochemistry.