|Abstract:||Some risks of having children at older ages are widely documented, and the “biological clock” is a popular media concern, but the association between cognitive disability generally and both mothers’ and fathers’ age is not well known. This paper assesses descriptively the relationship between children’s cognitive disability and parents’ age at birth, using a sample of 353,119 children aged 5 to 11 living with two married parents from the 2009-2011 American Community Survey. Cognitive disability varied by parental age categories from 1.8% to 5.4%, with overall rates of 2.2%. Odds of disability were much more strongly associated with mothers’ age at birth than with fathers’ age at birth, with highest odds for children whose mothers were age 45 or higher at the time of their birth (adjusted odds ratio 2.7 relative to age 30-34) and lowest for those born to mothers in their early 30s. These results demonstrate that the risk is strongly associated with mothers’ age at birth – but not fathers’. This is consistent with previous research showing that it is mothers’ health, rather than age per se, which is most important for the health of their children.