Background: The results of an open, single-center study suggested that phototherapy with high doses of UVA1 radiation (UVA1R; 340-400 nm) is effective for acute, severe exacerbations of atopic dermatitis (AD). Objective: The purpose of this study was to assess the effectiveness of high-dose UVA1 phototherapy for acute, severe AD in a randomized multicenter trial in direct comparison with topical glucocorticoid therapy. Methods: Patients were treated with high-dose UVA1R (10 days, 130 J/cm² /day; n = 20), topically with fluocortolone (10 days, 1 x daily; n = 17), or with UVA-UVB therapy (10 days, 1 x daily, minimal erythema dose–dependent; n = 16). Results: With a clinical scoring system, significant differences in favor of high-dose UVA1R and fluocortolone therapy were observed (p < 0.0001), as compared with UVA-UVB therapy. At day 10, high-dose UVA1R was superior to fluocortolone (p < 0.002) therapy. Serum levels of eosinophil cationic protein and the blood eosinophil count were significantly reduced after high-dose UVA1 or fluocortolone, but not UVA-UVB therapy. Conclusion: This study confirms the therapeutic effectiveness of high-dose UVA1 monotherapy for treatment of severe exacerbations of AD. (J Am Acad Dermatol 1998;38:589-93.)