A review of the world literature has revealed a total of 783 spontaneous neoplasms that have occurred in nonhuman primates, all similar to tumors in human beings. Carcinomas were the most frequently reported. Neoplasms occurred most frequently in older animals as they generally do in man. There were more reports on neoplasms in baboons and macaques than in other species. The digestive system was more commonly affected than were other organ systems.