Unilateral keratosis follicularis is considered a localized variant of Darier's disease and should be included in the differential diagnosis of diseases with zosteriform keratotic eruptions. It is characterized by the unilateral linear lesions in multiple locations, increased irritation by sweating, lack of solar aggravation, and negative family history. Histopathologic findings reveal acantholytic dyskeratosis similar to a generalized Darier's disease. We report a case of unilateral keratosis follicularis in a 68-year-old man, who presented with unilateral flesh-colored keratotic papules on the left axilla and inguinal area. He was effectively treated with oral 13-cis-retinoid acid (isotretinoin). (Kor J Dermatol 1996;34(1): 127-131)