To examine cumulative associations between midlife health behaviors and walking speed and upper-limb strength in early old age. Prospective cohort study. Whitehall II Study. Individuals (mean age 49.1 ± 5.9 in 1991-93) with health behavior data for at least two of the three assessments (1991-93, 1997-99, 2002-04) and physical functioning measures in 2007-09 (mean age 65.9 ± 5.9) (N = 5,671). A trained nurse assessed walking speed and upper-limb strength. Unhealthy behaviors were defined as current or recent smoking, nonmoderate alcohol consumption (abstinence or heavy drinking), fruit and vegetable consumption less than twice per day, and physical inactivity (<1 h/wk of moderate and <1 h/wk of vigorous physical activity). For each unhealthy behavior, a cumulative score was calculated as the number of times a person reported the behavior over the three assessments divided by 3. The score ranged between 0 (never) and 1 (all three times). In linear regression models adjusted for age, sex, education, marital status, and height, all unhealthy behaviors in 1991-93 were associated with slower walking speed in 2007-09, with differences ranging from 0.10 (nonmoderate alcohol consumption) to 0.25 (physical inactivity) of a standard deviation between participants with and without the unhealthy behavior (Pt-test <.001). For walking speed, the accumulation-of-risk model provided the best fit for unhealthy diet (β for a 1-point increment in the low fruit and vegetable consumption score = -0.29, 95% confidence interval (CI) = -0.36 to -0.22) and physical inactivity (β = -0.37, 95% CI = -0.45 to -0.29). For smoking and nonmoderate alcohol consumption, a cumulative effect was also observed, but partial F-tests did not suggest that it provided a better fit than models with behaviors in 1991-93, 1997-99, or 2002-04. All behavioral scores except smoking were associated with grip strength, but F-tests supported the accumulation-of-risk hypothesis only for physical inactivity. These findings highlight the importance of duration of unhealthy behaviors, particularly for diet and physical activity, when examining associations with physical functioning.