PIP: By examination of incidence, mortality, and relative frequency data, an estimate has been made of the number of cancer cases in 12 common sites and of all cancers that occurred in 1975 and in the 24 areas of the world for which the UN publishes population data. While several cancers are of importance in localized areas or regions; e.g., cancer of the larynx, these are infrequent on the world level and are not included here. While the relative importance of the selected sites varies from 1 area to another, on a global basis, the 1st 6 ranking cancer sites in males are lings, stomach, colon/rectum, mouth/pharynx, prostate, and esophagus; in females, they are breast, cervix uteri, stomach, colon/rectum, lung, and mouth/pharynx. Cancers of these sites, together with leukemias and cancers of the liver, bladder, and lymphatic tissues, account for 75% of the estimated 5.9 million cancers that occurred in 1975. When the 2 sexes are combined, stomach cancers are in 1st rank, followed closely by lung; it is suggested that, given current trends, their rank order will soon be reversed. There are clear opportunities for cancer prevention by controlling tobacco smoking, reducing infection by hepatitis B virus, and curbing the excessive intake of alcohol. The increasing adoption of high fat diets may lead to more cancers of the large bowel, breast, and prostate.