We investigated the circumstances of death and the medical and activity histories of 18 individuals who died during or immediately after jogging. Thirteen men died of coronary heart disease (CHD) and four men and one woman died of other causes. Six CHD subjects had medical histories relevant to the cardiovascular system, but only one had diagnosed CHD. Six CHD subjects experienced prodromal symptoms but continued vigorous exercise programs. Two subjects had exercised less than a month, but most had trained regularly for years. The CHD risk factors for the CHD cases did not differ significantly from those for other age-matched, physically active men. Superior physical fitness does not guarantee protection against exercise deaths. Physicians and exercising adults should be aware of this fact and give appropriate attention to possible prodromal symptoms.