Site-specific cancer incidence rates were computed by sex, age, and marital status for whites and blacks separately for ages 35-64 years with the use of population-based incidence data from the Third National Cancer Survey (1969-71) and with demographic data from the 1970 U.S. Census. Although rates were presented for all cancer sites combined and for 44 specific sites or rubrics, discussion focused on the 17 most common cancers. Within age, race, and sex groups, patterns of cancer incidence by marital status were compared by means of standardized incidence ratios, and the consistency of marital status patterns across age groups was assessed statistically. Among the most notable findings were: excess cancer rates across most sites and age groups in single black males, consistently high rates for cancer of the lung and bronchus in divorced white males and in single black females, low rates for the hormone-dependent reproductive tumors (prostate gland, breast, uterine corpus, and ovary) in separated white males and females, and high rates for cervical cancer among separated white women. Marital status patterns, where found, frequently differed between whites and blacks and between males and females.