IN THE past, the keratoses arising in senile or actinic skin were considered in the same category and not differentiated. The nomenclature and descriptions of these lesions caused confusion. More recent investigation has recognized two types,1 the senile (senile keratosis, keratoma senilis, hyperkeratosis senilis) and the seborrheic (seborrheic keratosis, verruca senilis, verruca seborrheica). With minor variation, this view has been accepted, and, while it does include the chief characteristics, some misunderstanding still remains, particularly as to the nomenclature. We feel that a further subdivision may be useful in formulating a clearer, more concise and more universal concept of the subject. Our studies and observations, over a period of many years, led us to conclude that there are four principal lesions, each with a distinct clinical and microscopic picture; the senile and seborrheic keratoses and the senile and seborrheic verrucae. The latter ones, respectively, develop from the former and represent