Background: UVA1 (340-400 nm) therapy proved to be highly effective in patients with severe atopic dermatitis. The optimal dose regarding therapeutic efficacy and possible side effects is still to be evaluated. In vitro cell culture as well as in vivo animal studies recently indicated that a correlation between UVA irradiation and photoaging, skin carcinogenesis, or melanoma induction may exist. Therefore it seems appropriate to focus research activities on reducing the UVA1 dose applied during phototherapeutic regimens minimizing nonbeneficial side effects. Objective: The present study was performed to evaluate the therapeutic effectiveness and long-term efficacy of medium-dose UVA1 irradiation in patients treated for acute exacerbated atopic dermatitis. Methods: Thirty-two patients underwent a medium-dose UVA1 therapy consisting of 15 treatments applied from Monday to Friday for a period of 3 weeks. The applied dose per treatment was 50 J/cm² resulting in a cumulative dose of 750 J/cm². Clinical severity was assessed according to the SCORAD index before and after irradiation as well as in monthly intervals up to 3 months after cessation of phototherapy. Results: Medium-dose UVA1 phototherapy is effective for alleviating acute exacerbated atopic dermatitis as shown by a significant reduction of SCORAD ratings (P < .001) at the end of the active UV treatment period. A significant skin improvement was still present 1 month later (P < .001). However, at the end of the 3-month posttreatment observation period the skin condition had reached the pretreatment level. Conclusion: According to our data, medium-dose UVA1 phototherapy is a highly effective, nonsteroidal, therapeutic alternative for treatment of acute exacerbated atopic dermatitis. However, effectiveness is merely short term, limited, and is followed by recurrence of symptoms within a 3-month observation interval. (J Am Acad Dermatol 2000;42:254-7.)