Paleo-oncology is the study of carcinomas and sarcomas in ancient human populations and their hominid precursors. These populations are informative concerning the possible influences on cancer of morphologic and functional evolution, diet, lifestyle, and other environmental factors.The prevalence of cancer in ancient populations might have differed from that in modern humans, because of substantial differences in tobacco and alcohol use, diet, life expectancy, and the availability of treatment. The available physical data concerning cancer in antiquity includes evidence of its existence in animal fossils and ancient humans and their precursors. The difficulties of paleo-oncologic research include a limited soft tissue record. In evaluating cancer in ancient remains, one must also deal with the problem of pseudopathology: whether an observed tissue change is an antemortem pathologic lesion or a postmortem artifact. Future archeological discoveries and the application of improved diagnostic techniques may enable paleo-oncology to make further contributions to our understanding of cancer.