The eruption, as a rule, begins slowly, usually showing itself upon the extremities; the forearms, wrists and legs being favorite localities. It may appear as one or more groups or in the form of short or long bands. Occasionally its evolution is rapid and a considerable part of the surface may be invaded. The lesions are pin-head to small pea-sized, irregularly grouped or so closely crowded together as to form solid patches; they are quadrangular or polygonal in shape, usually flat, with central depression or umbilication, and are reddish or violaceous in color. At first they have a glazed or shining appearance; later, becoming slightly scaly, the scaliness being more marked where solid patches have resulted. New papules may appear from time to time, the older lesions disappearing and leaving persistent reddish or brownish pigmentation. Exceptionally the eruption presents in bands or lines, like rows of beads (_lichen moniliformis_). Very exceptionally a vesicular or bleb tendency in some of the lesions has been noted; doubtless, in most instances at least, this has been due to the arsenic so generally administered in this disease. In rare instances lichen planus lesions are also seen on the glans penis and on the buccal mucous membrane. In some cases, especially in the region of the ankle, the papules become quite large (_lichen planus hypertrophicus_), and in occasional cases there is a tendency in some of the lesions or patches to clear up centrally. There is, as a rule, considerable itching. There are no constitutional symptoms. #What is the etiology of lichen planus?# In some cases the disease is distinctly neurotic in character, in others no cause can be assigned. It is more especially met with at middle age, and among the wealthier, professional, and luxurious classes. Pathologically the first change noted in the epidermis is thought to be an acanthosis, followed by epithelial atrophy, and a hyperkeratosis, intercellular edema, and colloid degeneration of the prickle cells. #Does the disease bear any resemblance to the miliary papular syphilide, psoriasis, and papular eczema?# In some instances it does, but the irregular and angular outline, the slightly-umbilicated, flattened, smooth or scaly summits, and the dull-red or violaceous color, the history and course, of lichen planus, will serve to differentiate. #State the prognosis.# Under proper management the eruption, although often obstinate, yields to treatment. #What treatment would you prescribe in lichen planus?#