The California Health Survey, a sample survey based on interviews with 10,000 households in the state, presents several opportunities for studying the epidemiology of chronic disease, and illustrates these. The Survey permits generalization of observations to the whole population within limits of confidence that can be stated, and provides a description of the population as a basis for studying the natural history of disease in that population. Limitations include the facts that diseases of infrequent occurrence cannot be studied, and that the Survey in effect excluded the institutional population with its high concentration of chronic disease. Uncertainty as to validity of some aspects of the data - particularly detailed diagnosis -presents another problem. Six specific contributions of the California Health Survey to the epidemiology of chronic disease are: demography, a broad picture of community health, extension of our knowledge of diseases themselves, data about utilization of health services, rosters of patients for detailed epidemiologic study, and data on causative factors in disease.