Tumor necrosis factor-related apoptosis inducing ligand (TRAIL) is a member of the tumor necrosis factor family that preferentially induces apoptosis in transformed but not normal cells and that is constitutively expressed in many organs including the skin. In addition to its therapeutic potential, TRAIL might act as a natural guardian eliminating transformed cells at an early stage. Ultraviolet (UV) radiation is not only a potent carcinogen because of its mutagenic effects but also because of its capacity to paralyze natural protection mechanisms, including the tumor suppressor gene p53. Therefore, we studied the effect of UV exposure on the expression of TRAIL in the skin by immunohistochemical analysis. TRAIL and its receptors TRAIL-R1 and TRAIL-R4 were constitutively expressed in normal epidermis and not altered in a variety of inflammatory dermatoses including those associated with interface dermatitis. TRAIL was not altered in biopsies of acute sunburn, polymorphic light eruption, and photoprovocation testing, indicating that acute UV exposure does not affect TRAIL expression. No differences were observed in UV-protected and chronically UV-exposed skin samples of younger adults. In contrast, TRAIL was significantly reduced in chronically UV-exposed skin of elderly individuals. In addition, TRAIL expression was reduced in actinic keratoses and Bowen disease and almost completely lost in basal cell and squamous cell carcinomas. In contrast, keratoacanthomas did not reveal any alterations in TRAIL expression. Taken together, these data indicate that chronic UV exposure in elderly patients results in the loss of TRAIL expression, which might contribute to the increased risk of skin cancer in this population. Down-regulation of TRAIL might represent another example of a natural protection mechanism that is eliminated by chronic UV exposure.