Two hundred specimens from lesions of lichen planus were studied by conventional light microscopy in order to assess their evolution, maturation, and regression. The most important finding was that Langerhans' cells appear in increased numbers in the epidermis very early in the disease, even preceding the experience of lymphocytes there and then that the appearance of lymphocytes is followed by destruction of keratinocytes in the lower portion of the epidermis and by general epidermal hyperplasia, including hypergranulosis and hyperkeratosis. Wedge-shaped hypergranulosis develops around intraepidermal adnexal structures, namely, acrosyringia and acrotrichia. Finally, long-enduring inflammatory-cell infiltration in the papillary dermis was found to result in eventual fibrosis there, an evidence of resolution. With time the inflammatory-cell infiltrate disappears and the epidermis regains its normal configuration. Bullous lichen planus, hypertrophic lichen planus, atrophic lichens planus, and lichen planopilaris are variants of the same pathological process, modified by intensity and location of process.