BACKGROUND: Previous research on developmental outcomes of infants with congenital heart disease (CHD) has shown delays in both cognitive and motor skills. AIMS: To describe outcomes on the Bayley Scales of Infant and Toddler Development, 3rd edition (Bayley-III) for infants with CHD and to compare those findings to published results for similar samples of infants assessed on the 2nd edition of the Bayley Scales (BSID-II). STUDY DESIGN: Prospective cohort. PARTICIPANTS AND OUTCOME MEASURES: Of 50 infants with CHD who participated in this longitudinal study (2006-2008) at the Royal Children's Hospital in Melbourne, Australia, 47 were assessed on the Bayley-III (median age=24.5 months), administered by a psychologist or neonatologist. Although neither assessor was blind to the CHD diagnosis, they were unaware of results of previous developmental assessments conducted in this longitudinal study. RESULTS: For the Bayley-III cognitive composite score, 17.0% of infants showed mild delays (1-2 SD below the mean), 2.1% had moderate delays (2-3 SD below the mean), and none had severe delays (greater than 3 SD below the mean). Motor composite scores showed mild delays in 10.9% of infants and moderate delays in 2.2%; none had severe motor delays. These findings differ from study results using the BSID-II in similar infants. CONCLUSIONS: The Bayley-III may underestimate developmental delay in 2-year-old children with CHD when compared to results of similar children tested at 12-36 months of age on the BSID-II.