Familial lichen planus is rare. As far as I can see its occurrence in twins, as presented here, has not been reported in the literature. REPORT OF CASE V. S., a white man, born Aug. 31, 1914, was first seen at the office on Jan. 13, 1939. He had noticed white lesions in the mouth about two months previously. Examination revealed typical lichen planus confined to the oral cavity. Numerous confluent reticular lesions covered nearly all of the mucous membranes of the cheeks. On the left side of the tongue, two oval annular lesions were present, unnoticed by the patient. The lips were not involved. No other lesions were found. The results of urinalysis and a blood count were normal, and the Wassermann reaction of the blood was negative. Six months later, after the intake of 60 cc. of solution of potassium arsenite U. S. P., the eruption cleared up