The authors examined associations of health behaviors over a 17-year period, separately and in combination, with cognition in late midlife in 5,123 men and women from the Whitehall II study (United Kingdom). Health behaviors were assessed in early midlife (mean age = 44 years; phase 1, 1985-1988), in midlife (mean age = 56 years; phase 5, 1997-1999), and in late midlife (mean age = 61 years; phase 7, 2002-2004). A score of the number of unhealthy behaviors (smoking, alcohol abstinence, low physical activity, and low fruit and vegetable consumption) was defined as ranging from 0 to 4. Poor (defined as scores in the worst sex-specific quintile) executive function and memory in late midlife (phase 7) were analyzed as outcomes. Compared with those with no unhealthy behaviors, those with 3-4 unhealthy behaviors at phase 1 (odds ratio (OR) = 1.84, 95% confidence interval (CI): 1.27, 2.65), phase 5 (OR = 2.38, 95% CI: 1.76, 3.22), and phase 7 (OR = 2.76, 95% CI: 2.04, 3.73) were more likely to have poor executive function. A similar association was observed for memory. The odds of poor executive function and memory were the greater the more times the participant reported unhealthy behaviors over the 3 phases. This study suggests that both the number of unhealthy behaviors and their duration are associated with subsequent cognitive function in later life.