There are no population-based studies on cancer in Saudi Arabia, where lung cancer is readily emerging as a common cancer-related death. This work is aimed at describing the incidence of lung cancer in the population of the Eastern Region of Saudi Arabia. A population-based tumor registry was established in 1987. Data on all cancer sites were captured from all 22 hospitals in the Eastern Region. The population census for 1988 was derived from a doorto-door survey. Relative frequency rates were used to compare our data with nationally reported data derived from hospital-based registries. Crude incidence rates, age-specific incidence rates, age-standardized rates adjusted to the world standard population, and relative age-standardized rates were used for international comparisons. A total of 107 cases of primary lung cancer were registered in 1987 and 1988. Saudis constituted 80% of these cases. The observed overall relative frequency rate of 6.9% was the highest in Saudi Arabia. Similarly, the relative frequency rates among males of all nationalities (9.8%), Saudi males (10.7%), and Saudi males registered from the Dhahran Health Center (15%) were higher than those reported in other regions in Saudi Arabia. The relative frequency rate among Saudi females registered from the Dhahran Health Center (7.3%) was significantly higher than that from other regions in Saudi Arabia. Among Saudi males, lung cancer was the leading cause of cancer death (25.6%), and the second cause (9.7%) among Saudi females in the Eastern Region. The crude incidence rate of lung cancer per 100,000 population per year was 6.5 for Saudi males and 1.3 for Saudi females. The age-standardized rates per 100,000 population per year were 16.5 for Saudi males and 4.0 for Saudi females. Among Saudi males, cancer of the lung was the leading cause of morbidity and mortality from cancer of all sites. The relative frequency rate of lung cancer has increased among cancer patients from Saudi ARAMCO's Dhahran Health Center during the past 40 years. This is attributed to an increased number of tobacco smokers and increased environmental pollutants from industry and gasoline-driven vehicles. The crude incidence rate and age-standardized rate of lung cancer in the Eastern Region are very low compared with those reported from developed countries. This can be explained by the young Saudi population in the Eastern Region, and the relatively recent history of cigarette smoking and industrialization in Saudi Arabia. A plea is made for a smoke-free society and a cleaner environment to prevent the incoming creeping epidemic of lung cancer.