Background: It is inconclusive on how sex affects the risk of developing mild cognitive impairment (MCI) or dementia. Objective: To investigate how sex affects the risk of developing MCI or dementia. Methods: A secondary data analysis was performed on data collected from participants enrolled at Alzheimer's Disease Research Centers funded by National Institute on Aging. There were two inclusion criteria: 1) participants were free of dementia at the baseline visit; 2) every participant must have at least one follow-up visit. A Cox proportional hazards model was used to investigate how sex affects the risk of developing cognitive impairments. Results: During a follow-up period of more than 10 years, male participants had a slightly higher incidence than female participants for either MCI or dementia. Not surprisingly, a higher prevalence was observed in male than female participants for either MCI or dementia. However, male participants had a higher mortality rate than their female counterparts. Conclusion: The male sex is associated with a higher risk for developing cognitive impairments along the aging process.