Many experimental, clinical and epidemiological data indicate that n-3 and n-6 essential fatty acids are therapeutic nutrients which may delay the development as well as improve the course of cancer. The present hypothesis correlates well with these data and it is proposed that chronic essential fatty acid deficiency, when coexisting with chronic hyperproliferative states (hyperplasias) and de-differentiation (dysplasias) both acting synergistically, may constitute a pro-tumorigenic situation. Evidence showing that, indeed, these hyperproliferative states are consistently reported in essential fatty acid deficiency in many species, including humans, in malpighian layers of skin and the upper alimentary and urinary tracts, among others, is discussed.