Objective: Income volatility presents a growing public health threat. To our knowledge, no previous study examined the relationship between income volatility, cognitive function and brain integrity. Methods: We studied 3,287 participants aged 23 to 35 years in 1990 from the Coronary Artery Risk Development in Young Adults prospective cohort study. Income volatility data were created using income data collected from 1990 to 2010 and defined as standard deviation of percent change in income and number of income drops >=25% (categorized as 0, 1, or 2+). In 2010, cognitive tests (n=3,287) and brain scans (n=716) were obtained. Results: After covariate adjustment, higher income volatility was associated with worse performances on processing speed (β=-1.09, 95%CI=-1.73, -0.44) and executive functioning (β=2.53, 95%CI:0.60, 4.50) but not on verbal memory (β=-0.02, 95%CI:-0.16, 0.11). Similarly, additional income drops were associated with worse performances on processing speed and executive functioning. Higher income volatility and more income drops were also associated with worse microstructural integrity of total brain and total white matter. All findings were similar when restricted to those with high education, suggesting reverse causation may not explain these findings. Conclusion: Income volatility over a 20-year period of formative earning years was associated with worse cognitive function and brain integrity in midlife.