Biliary atresia is a rare birth defect that affects 1 in 12,000 to 1 in 19,500 live births. We used data from the National Birth Defects Prevention Study, a multistate case-control study, to identify potential risk factors for isolated biliary atresia (no additional unrelated major birth defects diagnosed). Infants were identified from eight states from 1997 to 2002, with clinical information abstracted from medical records. Potential risk factors assessed include: demographic factors, seasonality, preterm birth, maternal smoking, maternal alcohol use, maternal illicit drug use, maternal health, maternal medication use, maternal vitamin use, and maternal nutrition. Infants of non-Hispanic black mothers were more likely to have biliary atresia than infants of non-Hispanic white mothers (adjusted odds ratio (aOR) = 2.29, 95% confidence interval (CI) 1.07-4.93) and infants conceived during the spring season were more likely to have biliary atresia than infants conceived in winter (aOR = 2.33, 95%CI 1.05-5.16). Low intakes of vitamin E, copper, phosphorus, and beta tocopherol were associated with the occurrence of isolated biliary atresia (borderline significance). Low iron intake had a borderline inverse association with biliary atresia. While this analysis provides support for previous reports of a possible association between seasonal variation and the occurrence of biliary atresia, more data are needed to evaluate whether the seasonal variation is related to infectious agents. The role of nutrients in the development of biliary atresia remains unclear. Further studies of genetic, infectious, and nutrient exposures and the association of biliary atresia are warranted.