BACKGROUND: Muenke syndrome is a genetically determined craniosynostosis that involves one or both coronal sutures. In some patients it is associated with skeletal abnormalities such as thimble-like middle phalanges, coned epiphysis, and/or neurological impairment, namely sensorineural hearing loss or mental retardation. In spite of a variable phenotype, Muenke syndrome has been related to a unique mutation on the FGFR3 gene, Pro 250 to Arg, which is characteristic of this disease. Because of the incomplete penetrance of this anomaly, the suspicion of Muenke syndrome must be raised in any child with uni- or bilateral coronal craniosynostosis, and the genetic analysis propounded even in the absence of extracranial features. ILLUSTRATIVE CASES: We report the cases of two sisters who presented with Muenke syndrome and whose affected mother did not have any form of craniosynostosis.