The effect of cranial release and reconstruction on the mental development of infants with nonsyndromic craniosynostosis was evaluated. Longitudinal assessment of mental development for infants before and after cranial release and reconstruction and for infants not undergoing surgical treatment was obtained by using the mental scale of the Bayley Scales of Infant Development. Severity of anatomic craniofacial deformity, perinatal medical risk factors, and age at time of surgery also were investigated. None of the infants displayed mental retardation [Mental Development Index (MDI) score < 70] before or after cranial release and reconstruction. Scores ranged from borderline retardation to very superior following a normal distribution. Severity of anatomic craniofacial deformity and perinatal risk factors were unrelated to mental development. Cranial release and reconstruction did not affect mental development positively or negatively but did result in improvement of the original craniofacial deformity.