A patient with fluoroscopy-induced subacute radiation dermatitis is described. Her biopsy specimen showed vacuolar change and necrotic keratinocytes with lymphocytes in direct apposition, or “satellitosis.” Lymphocytes in the dermis and infiltrating the epidermis were predominantly CD8⁺ and a number of the lymphocytes stained for TIA-1, a cytotoxic granule protein in T-cells and natural killer cells, that appears to be involved in the induction of apoptosis. Our findings suggest cytotoxic lymphocyte mediated apoptosis is involved in the pathogenesis of subacute radiation dermatitis. (J Am Acad Dermatol 1998;38:333-6.)