Background: The results of a recent study suggested that ultraviolet A1 radiation (UVA1R; 340-400 nm) phototherapy for atopic dermatitis works through induction of apoptosis in skin-infiltrating helper T cells, indicating the possibility that other helper T cell–mediated skin diseases may respond to UVA1R as well. Objective: The purpose of this open pilot study was to assess the therapeutic effectiveness of UVA1 phototherapy for cutaneous T-cell lymphoma (CTCL). Methods: UVA1 phototherapy was used as monotherapy in patients (n = 3) with histologically proven CTCL (stages IA and IB). For daily whole body UVA1 irradiations, either a high-dose (n = 2; 130 J/cm² UVA1 per exposure) or medium-dose (n = l; 60 J/cm² UVA1) regimen was used. Therapeutic effectiveness was assessed clinically and histologically. Results: In each of the 3 patients, skin lesions began to resolve after only a few UVA1 radiation exposures. Complete clearance was observed between 16 and 20 exposures, regardless of whether the high- or medium-dose regimen had been employed. Conclusion: These studies suggest that patients with CTCL stages IA and IB can be treated effectively with UVA1 phototherapy. (J Am Acad Dermatol 1999;41:47-50.)