SummaryThe distinctive clinical and histological features of an extensive case of hyperkeratosis lenticularis perstans and the rapid and complete response to topical applications of betamethasone‐17‐valerate are recorded. No previous record of effective treatment has been described in the four male cases previously recorded in the literature.A 57 year old female has also been studied with a twenty year old history of an unremitting progressive eruption showing the clinical and histological features of hyperkeratosis lenticularis perstans. In this patient initial response to topical therapy with betamethasone‐17‐valerate is most gratifying, and is the first treatment to influence the signs and symptoms of the diseas