We measured mental and motor development in 27 infants and 14 children with end-stage biliary atresia who were awaiting liver transplantation, and we measured disease-related variables (physical growth, liver function, and severity and duration of disease) that may relate to development. We then determined the relationship between development and the disease-related variables. Infants were assessed with the Bayley scales, and children were assessed with the Stanford-Binet scales of intelligence and the Minnesota Child Development Inventory. The mean +/- SD mental and motor scores for infants were 79.5 +/- 19.6 and 69.7 +/- 17.6, respectively. The mean +/- SD IQ and motor development scores for children were 76.1 +/- 16.6 and 56.9 +/- 18.1, respectively. For infants, mental and motor development were related significantly to height and weight (r values ranged from .42 to .72). Mental development in infants was also related significantly to serum vitamin E levels (P = .03). Multiple regression analyses combining growth and disease-related indices predicted 70% of the variance in mental and motor development in infants (P = .001). For children, development was related to measures of liver function (ie, to serum bilirubin, r = -.51, P = -.08, and to serum albumin, r = .54, P = .06) but not to growth. Careful nutritional support during infancy and aggressive management of liver disease prior to transplantation may be important in optimizing the development of children with biliary atresia who subsequently undergo liver transplantation.