Urban-rural differences in cancer incidence and mortality rates were evaluated in a descriptive epidemiologic study among Iowa residents (1973-1988). Results were based on two separate definitions of urban and rural-one county boundary based and the other based on application of an address algorithm. Both definitions yielded similar findings. Two different definitions of mortality were used. The first definition included as an eligible death only those cases where cancer was listed as the underlying cause of death , whereas the second definition included all conditions of cancer where cancer was listed on the death certificate as the underlying cause or as a contributing condition. Study findings were 1) Smoking-related cancers were found to be significantly higher in urban areas relative to rural areas for males and females, and mortality from smoking-related cancers was greater in urban areas; 2) Lip cancer in males was the only cancer site with a significantly elevated rate in rural areas relative to urban areas, all other cancers were higher for urban areas, for both males and females; 3) Better sensitivity was established when using the 'all causes of death' definition, and use of the application algorithm proved more sensitive as well; and 4) Cancer mortality rates were generally higher in those urban and rural areas that had higher cancer incidence rates. An additional research project was funded by the National Cancer Institute to investigate these findings further. Technical Report Available.