PR intervals of 0.22 sec or longer were detected in the electrocardiograms of 95 of 4,678 participants past 20 years of age in the Tecumseh Community Health Study. The prevalence rates were similar in men and women and remained low through the sixth decade, but increased sharply in succeeding decades. Nineteen of the 95 persons had some other manifestation of heart disease and there was a significant association between delayed atrioventricular conduction and angina pectoris or asymptomatic T wave inversion in participants past 60 years of age. Most of the cardiac abnormalities were found among older individuals. Atrioventricular block was more constant on second examination in this group and may have been due in part to sclerosis of the left side of the cardiac skeleton, as well as specific etiologic types of heart disease. Among younger and apparently healthy participants the PR interval usually shortened on repeat examination, frequently to less than 0.22 sec. There was no excess incidence of cardiovascular disease or mortality among the persons with long PR intervals during a mean period of observation of four years. Delay in atrioventricular conduction by itself appears to be a benign condition with no unfavorable prognostic significance. It is probably a transient finding among many members of the population.