38 biopsies of perioral dermatitis have been examined. The following has consistently been observed: follicular hyperkeratosis; vasodilatation and oedema (sometimes very pronounced) of the papillary dermis; peri vascular and parafollicular infiltrates consisting predominantly of lymphocytes, histiocytes and polymorphonuclear leucocytes. Occasionally, there have been epithelioid or giant cells, sarcoid-like infiltrates or vasculitis of the leucoclastic type. Demodexfolliculorum was observed in only two sections and the follicles that contained them were not inflamed. This histological picture is very similar to that of acne rosacea.