Skull deformity in infants continues to be a diagnostic and therapeutic challenge. Deformational plagiocephaly is a common and somewhat benign cause of skull deformity in infants that must be distinguished from the more serious craniosynostosis, which occurs alone or as a syndrome. Examining an infant's head from above can help the physician distinguish true lambdoid synostosis from deformational plagiocephaly. In infants with lambdoid synostosis, the posterior bossing is in the parietal area contralateral to the flat part of the head. Deformational plagiocephaly causes frontal bossing ipsilateral to the flat part of the head. In infants with lambdoid synostosis, the ear is displaced posteriorly toward the fused suture. In infants with deformational plagiocephaly, the ear is displaced anteriorly. Isolated sagittal synostosis is the most common type of craniosynostosis. Of the more than 150 craniosynostosis syndromes, Crouzon's disease and Apert's syndrome account for the majority of cases. The diagnosis of craniosynostosis relies on physical examination, plain radiography, and computed tomography. Untreated progressive craniosynostosis leads to inhibition of brain growth, and an increase in intracranial and intraorbital pressure. Infants should be evaluated as soon as they are diagnosed.