The current study employed a within-family adoption design to examine the genetic and environmental influences on general cognitive ability. A sample of 51 families with biological (mean age = 9.83 years, S.D. = 2.81) and adoptive children (mean age = 6.86, S.D. = 1.92) was selected from the larger "Northeast-Northwest Collaborative Adoption Projects" [Deater-Deckard, K., Petrill, S.A., & Wilkerson, B. (2003). "The Northeast-Northwest Collaborative Adoption Project: Identifying family environmental influences on cognitive and social development" (pp. 157-178). In K. Deater-Deckard & S. A. Petrill (Eds.). "Gene-environment processes in social behaviors and relationships." New York: Haworth Press]. Parents and children were assessed using a shortform of the "Stanford-Binet Intelligence Scale" [Thorndike, R.L., Hagen, E.P., & Sattler, J.M. (1986). "Guide for administering and scoring the fourth edition: Stanford-Binet Intelligence Scale." Chicago, IL; Riverside]. Mothers were significantly correlated with their biological children (r = 0.23) but not their adoptive children (r = -0.03). These results suggest that genetic and nonshared environmental influences are significant, whereas shared environmental influences are nonsignificant. However, adoptive children's cognitive skills were predicted by age of placement and number of years in the home, suggesting that other nongenetic factors not related to maternal cognitive ability may be operating.