To the Editor: In patients with acanthosis nigricans the skin of the back of the neck, axillary folds, belt line and creases over the dorsal surface of the fingers becomes velvety and hyperpigmented. These changes occur in some patients with obesity of long duration, endocrine disorders or neoplasia (M Lerner: Clinical Dermatology. New York, Harper and Row, 1974). How patients with such different conditions acquire the same cutaneous picture is not known. In a previous letter to the editor (N Engl J Med 281:106, 1969) we proposed a hypothesis to explain the appearance of acanthosis nigricans in patients with endocrine . . .