Regular physical activity decreases the mortality rate in middle-aged men and probably in middle-aged women. It is unknown whether this is also true in the elderly. We studied 285 men and women aged 75 years or older who were free of cardiovascular disease. Subjects were ranked by baseline physical activity levels and grouped into quartiles. After adjustments were made for cardiac risk factors, chronic obstructive pulmonary disease, and cancer, women in the second most active quartile had a much lower risk of mortality at 10 years (relative risk 0.24, 95% confidence interval 0.12 to 0.51). There was no statistically significant difference in men. There appeared to be an excess of sudden cardiac deaths in the most active women, although this group still lived longer than the least active women. We conclude that women aged 75 years or older who are more active live longer. This benefit may be attenuated in those who are extremely active.