Despite intense research, etiologies underlying syndromic craniosynostosis remain poorly understood. While syndrome-related genetic factors have garnered much attention, external forces likely play a large role as well. In contrast to well-defined genetic abnormalities that may be precisely identified and statistically quantified, characterization of more environmental factors has proven difficult. Much of this challenge stems from difficulty in isolating genetic components. However, in the event that 2 individuals share similar genetics, a clearer picture of external factors impacting phenotypic differences may be drawn. Because monozygotic discordant twins have identical genomes, the differences between affected and unaffected members are the result of the environment. Here, we discuss identical twin females who presented with Crouzon syndrome, as well as variations in craniosynostosis. In addition to highlighting the impact of nongenetic factors on craniosynostosis phenotype, we review several environmental elements that may have played a role in this unusual case.