Cross-sectional and longitudinal age-associated reductions in power and isometric strength are described for the upper extremities. Over a 25-year period, repeated measures were taken approximately every 2 years from men and women in the Baltimore Longitudinal Study of Aging (BLSA). The longitudinal measures covered an average 9.6 years, range 1-25 years for men and an average 4.6 years, range 1-8 years for women. Strength and power declined beginning by age 40 in both women and men. Thereafter, power declined about 10% more than strength in men, while no significant differences were found in women. Age had a statistically independent influence on strength and power measures after adjusting for gender, height, weight, caloric expenditure, and muscle mass. Twenty-five-year longitudinal analyses in men confirmed the declines observed cross-sectionally, while no changes were observed in women over the 4-5 years of longitudinal data available. Further longitudinal studies are needed to understand the relationships between strength and power losses with age in women. The differences between power and strength changes with age in men argue for the importance of factors other than strength affecting power.