The mortality of foundry workers was studied from a sample of all those men employed in 20 representative iron, steel, and nonferrous foundries for any period of time during 1950 through 1972. A statistical sample of 3,876 men from all those 15,401 workers with at least 3 months' exposure formed the cohort under study. The actual number of person-years of follow-up became 47,160. Total and cause-specific mortality was studied in the entire cohort and in different categories based on exposure time and occupation. The foundry workers' experience was compared to that expected on the basis of the general male population's death rates in Finland, and different categories of the cohort were compared to each other through direct standardization. During the period from 1950 through 1973, there had occurred 224 deaths. The mortality approached the expected value computed from the age-adjusted general male population, the standardized mortality ratio (SMR) being 90 for all foundry workers and 95 for workers in "typical" foundry occupations. The corresponding standard mortality ratios based on the estimated total number of person-years, after the application of corrections for sampling fractions, were 86 and 95, respectively. There was a slight shift of the age of death towards younger age groups among the casters, fettlers, and furnace tenders. Mortality from coronary heart disease showed a standardized mortality ratio of 80 for the whole cohort; no significant differences were found for any occupational category. Lung cancer mortality was higher than expected (SMR 150) in the entire cohort; closer analysis revealed that the excess was confined to iron foundries, and especially to molders with more than 5 years of exposure. There were no more violent deaths than expected, not even from work accidents. Because most occupational cohorts have standardized mortality ratios that are well below 90, the present results were interpreted as probably indicating slightly elevated mortality. The most important finding was the concentration of lung cancer among molders in iron foundries.