This paper analyzes age-specific trends in brain and other central nervous system cancer mortality from 1968 to 1987 in several major industrial countries. It also examines changes in the use of diagnostic confirmation technology and trends in incidence in the U.S. National Cancer Institute, Surveillance, Epidemiology, and End Results (SEER) program from 1973 to 1987 to estimate the influence of diagnostic factors on recent mortality trends. Other sources of error have not been evaluated in this paper. Age-specific analyses of brain and other nervous system cancer mortality show drastic increases in persons ages 75-84 and consistent increases in younger age groups in most countries, although mortality declined in the U.S. in persons 0-24 by 2% annually. In the SEER program, brain cancer incidence increased significantly by 2%, 1%, and 5% annually in persons aged 0-44, 65-74, and 75-84, respectively. Throughout this time period, microscopic or radiographic confirmation occurred in at least 96% of all incident cases of brain and other central nervous system cancers diagnosed before death, with older persons receiving consistently more radiographic tests than younger persons. Changes in diagnoses across populations and over time are unlikely to account completely for these increasing trends which are occurring simultaneously in both males and females in major industrial countries. Additional studies need to be conducted, to exclude artifacts, to assist health care planners in anticipating treatment demands, and to detect preventable causes of these changing trends.