The basis for primary prevention of cancer is well-established, because significant causes of cancer are known. However, apart from reducing cigarette smoking, few easily applicable measures to decrease cancer incidence are available. Recently, there has been much interest in chemoprevention in cancer control, with several international bodies, including the International Union Against Cancer (UICC) and the European Union (EU), making important contributions. The results and relevance of these studies are discussed. Many of the problems associated with evaluating cancer prevention strategies generally apply particularly to chemoprevention, and these issues also are addressed.