A 32-year-old woman and her 35-year-old sister presented with plaques of scleroderma en coup de sabre. The younger sister's disease was more severe and preceded the older sister's by 10 years. This is the second reported case of familial en coup de sabre, and the first case of horizontal transmission. Treatment of the younger sister with antimalarials and narrow-band ultraviolet B (NB-UVB) phototherapy slowed disease progression and reversed hair loss. The observation that NB-UVB was effective in this case of linear scleroderma suggests that it may be indicated as a therapy for cutaneous scleroderma.