17 patients with palmoplantar keratoderma (PPK) were detected among 48 investigated members of the clan O. 5 of these 17 patients had a well-expressed hyperkeratosis on their knees. In one family hyperkeratosis of the knees was inherited as a dominant feature, but in two other families it was not. The observation was made that the expressivity of the disease was fading: while there were 15 PPK patients among the 25 investigated members in the generations II and III, there were only 2 patients among 22 members in the generations IV and V. In addition to PPK incontinentia pigmenti was diagnosed in two instances and pollex duplex in one. The question of the identity of PPK of Greither’s type is shortly discusse