The authors assessed the association between cognitive function and incidence and maintenance of overweight in preschool children. A population-based birth cohort was established in Menorca, Spain, between 1997 and 1999 (n = 482). Body mass index (weight (kg)/height (m)(2)) was measured at ages 4 years and 6 years (n = 421). At age 4 years, children were assessed for cognitive function (McCarthy Scales of Children's Abilities) (n = 395). After multivariable adjustment for a wide range of factors, including maternal education and body mass index, children with higher general cognition at age 4 years had a lower likelihood of being overweight (odds ratio = 0.47, 95% confidence interval (CI): 0.25, 0.88) at age 6 years. Children with higher general cognition at age 4 years had a lower likelihood of maintaining an unhealthy weight status (being at risk of overweight or overweight) between ages 4 years and 6 years, as well as worsening weight status over time, than children who maintained a healthy weight (odds ratios were 0.78 (95% CI: 0.54, 1.14) and 0.77 (95% CI: 0.51, 1.14), respectively). When specific dimensions of cognitive function were assessed, associations were mainly found for verbal and executive function areas. Children with higher cognitive function in early life might be at decreased risk of overweight later in childhood.