Palmoplantar keratoderma is a group of hereditary disorders of keratinization involving hyperkeratosis of palms and soles. Two different forms of palmoplantar keratoderma have recently been shown to be caused by mutations in the body site-specific keratin 9 gene and in the keratin 1 gene, respectively. Now we have analyzed a large German family with autosomal dominantly inherited palmoplantar keratoderma in association with carcinoma of the esophagus. Linkage to both the type I keratin gene cluster on chromosome 17q distal to the type I keratin genes. Two-point linkage data at D17S801 gave a lod score Zmax - 5.1 at theta = 0.00. Therefore, palmoplantar keratoderma is shown to be heterogeneous clinically as well as genetically and may be caused by mutations in keratins as well as in nonkeratins.