A total of 7251 histologically confirmed new cases of cancer (4117 males and 3134 females) were seen in the 6-year period 1979 to 1984 at the King Faisal Specialist Hospital and Research Centre in Riyadh, Saudi Arabia. The crude relative frequencies of cancer at various primary sites have been determined with reference to sex, age, geographic origin, and year of diagnosis. The most common cancer sites among males were non-Hodgkin's lymphomas, esophagus, lung, liver, stomach, and nasopharynx. Breast cancer was the most common tumor among the females, followed by non-Hodgkin's lymphomas and cancers of the thyroid, esophagus, cervix, and ovary. The most marked deviations were found in the Southern Region for cancers of the oral cavity (2.4 times higher), bladder (1.8 times higher), and lung (4.3 times lower). Known etiologic factors, such as local chewing, smoking habits, and schistosomiasis are likely to be responsible for these differences. Upward trends in cancers of lung, breast, colon and rectum, and the downward trend in esophageal cancer may reflect the rapid pace of modernization.