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Notes: This study describes a family of 30 people in which 14 members have hereditary epidermolytic palmoplantar keratoderma. Four patients were treated with an oral aromatic retinoid for up to 5 months. They responded in a uniform and dramatic way: 10-14 days after the onset of therapy, the hyperkeratotic horny layer was sequestered in large sheets resulting in normal appearing skin and restoration of normal surface sensitivity. Biopsies revealed that the underlying disorder of keratinization had remained unchanged. Treatment with the retinoid had to be discontinued as the sensitivity and vulnerability restricted normal function of hands and feet.Epidermolytic hyperkeratosis (Frost & Van Scott, 1966) is a disorder of keratinization with distinctive histopathological (Ackermann, 1970; Frost & Van Scott, 1966; Lapière, 1932; Lapière, 1957) and ultrastructural (Anton-Lamprecht & Schnyder, 1974; Lapière, 1932; Lapière, 1957) characteristics which may be found in genetically transmitted diseases, certain types of naevi and hamartomas (Ackermann, 1970; Gebhart & Kidd, 1973; Plewig & Christophers, 1975; Schnyder, 1970) or, as an accidental feature, in a variety of acquired hyperkeratotic skin conditions (Ackermann, 1970; Plewig & Christophers, 1975). As a genodermatosis, epidermolytic hyperkeratosis in generalized expression presents as bullous ichthyosiform erythroderma (Frost & van Scott, 1966; Lapière, 1932; Lapière, 1957), but localized manifestations may assume the clinical appearance of hereditary linear naevus or hereditary palmoplantar keratoderma. In these localized lesions, the propensity to form bullae is minimal or absent. The epidermolytic variants of linear naevi and palmoplantar keratoderma thus do not differ appreciably from the common orthohyperkeratotic types, and the diagnosis is often made on an incidental basis.Although estimates of its incidence are a matter of speculation, epidermolytic hereditary palmoplantar keratoderma (EHPPK) appears to be exceedingly rare. Hitherto, only four affected families (Klaus, Weinstein & Frost, 1970; Voerner, 1901) and one single case (Brunsting et al., 1962) have