Epidemiologic observations indicate that environment and lifestyle are the major determinants of the geographical patterns of cancer. The developing countries, which account for 75% of the world's population, have lower incidence rates of cancer compared with the industrialized nations but bear more than half the global cancer burden. Demographic trends resulting from economic progress (decreasing incidence of infectious diseases, population growth, aging, and urbanization), coupled with increased tobacco consumption and dietary changes, indicate that developing countries will bear a continually increasing proportion of the world's cancer burden and its accompanying demand for the provision of costly treatment programs. Yet the developing countries command only 5% of the world's economic resources, and health care programs are already fully extended and frequently inadequate. Thus, cancer control in the developing countries, including preemptive prevention of the anticipated increases in cancers presently more common in the industrialized nations (e.g., lung, breast, and colon), should include much greater emphasis on cancer prevention than is presently the case. But there is another perspective. The developing countries, with their dramatic contrasts in lifestyles and environments and equally diverse patterns of cancer, provide an unparalleled, and often neglected, opportunity for studies directed toward understanding the mechanisms of environmental carcinogenesis. Such an understanding should eventually lead to the development of novel intervention approaches. Unfortunately, cancer research is much more difficult to conduct in the developing countries because of the lack of population-based registries, poor communication and transportation systems, and deficiencies in infrastructure, financial support, and the training of health professionals. These difficulties could be overcome, to the benefit of all, if the extent of collaboration in cancer research between the developing and industrialized nations were to be greatly expanded.