Abstract Background Medium‐dose ultraviolet light A – 1 ( UVA ‐1) phototherapy, given in short courses, has shown efficacy in atopic dermatitis flares; little is known about its use, efficacy, and side effects in prolonged exposure used in the chronic disease despite its extensive use. Methods A descriptive retrospective study was conducted; convenience sampling of patients with atopic dermatitis treated with UVA ‐1 phototherapy was made; evaluation of clinical response by SCORAD , adverse effects, and protocols used in each patient were evaluated. Results Patients exposed to UVA ‐1 phototherapy showed a decrease in the SCORAD (30.1 points) – total cumulative dose‐dependent ( P < 0.0001) – regardless of multiple variables studied. There were low rates of relapse and adverse effects. The most frequent doses were 30 and 60 J/cm 2 , three times per week; patients had similar clinical responses and adverse effects in these groups independent of the other variables studied ( P = 0.057). Conclusion UVA ‐1 phototherapy can be an alternative for patients with severe atopic dermatitis even at lower doses than those described in other series (30 J/cm 2 ) and not only for acute flares. Cumulative total dose is a variable that affects the clinical response directly. Large prospective studies are needed.