As many as half of all sudden cardiac deaths are unexpected, with no preceding symptoms or signs of cardiac problems. Since 1948, the Manitoba Follow-up Study has prospectively recorded routine medical information and resting electrocardiographic (ECG) findings from a cohort of 3983 men. During 58 years of follow-up, 180 men experienced sudden unexpected cardiac death (SUCD). Heart rate, the longest QT interval, the shortest QT interval, and their difference and QT dispersion (QTD) on ECGs recorded prior to SUCD and 5 years and 10 years earlier were compared with QT intervals on ECGs of age-matched controls. QTD and heart rate each were significantly (P < .01) and independently associated with increased risk for SUCD. Only primary prevention can reduce the risk for SUCD. Hence, this relationship between QTD and heart rate and SUCD emphasizes the importance of longitudinal noninvasive QT measurements on routine ECGs in healthy men.