The current study compared the mental and psychomotor development of infants with nonsyndromic sagittal synostosis (SS) with a demographically matched comparison group without congenital defects. Within the SS group, we tested the hypothesis that age of cranial release would be inversely correlated with mental development.The design was prospective and longitudinal. Participants were assessed at 4, 12, and 24 months of age.The study was conducted in a craniofacial clinic at an urban children's hospital.Participants were 19 infants with SS (consecutive craniofacial program referrals) and 19 demographically matched comparison infants recruited from the community. One infant with SS did not attend the 24-month assessment.Mental and Psychomotor Indices from the Bayley Scales of Infant Development were the primary outcome measures. Subdomains of development were created using Kohen-Raz scoring procedures. All measures were determined a priori.Repeated-measures MANOVAs revealed no statistically significant differences in the developmental trajectories of the two groups. None of the SS group infants received Mental Development Index (MDI) scores in the mentally retarded or borderline range of intellectual functioning (i.e., below 78). An inverse correlation (r = -.30) was found between the age at surgery and Bayley growth curve coefficients; however, this association was not statistically significant (p = .10, one-tailed).Results are consistent with previous studies of the mental and psychomotor development of infants with nonsyndromic craniosynostoses in relation to normative test data. The relation between surgery age and developmental outcome merits further study in a larger sample with a greater range of surgery ages.