No national data exist on the prevalence of cancer in the United States population. The authors report the first estimates of prevalence rates of cancer from a population-based sample of the adult population of the United States. Estimates are based on responses collected from the Cancer Control Supplements of the National Health Interview Survey, a population-based sample survey of all people older than 17 years of age in the United States in 1987. Of 44,123 adults questioned, 1593 said they had a nonskin cancer. In 1987, after adjustments, the overall prevalence rate of all types of cancer, excluding nonme-lanoma skin cancer, was 3230 per 100,000 adults; the rates for men and women were 1930 and 4412, respectively. The authors estimate that, in 1987, 5.7 million adults in the United States were survivors of nonskin cancer, 3.3% of the adult population. Approximately 89,000 adults had cancer during childhood, or 1.6% of the total. Approximately 3.6 million people were at least 5-year survivors and 900,000 adults had their disease diagnosed during the year before interview. Despite the potential for underreporting and misclassification, these national estimates are in general accord with figures estimated from other sources. Increasing survival after cancer, especially childhood and adolescent cancer, indicates the importance of continued monitoring to provide information needed to plan for adequate health services.