The causative relationship between several of the syndromic forms of craniosynostosis and mutations in the fibroblast growth factor receptor (FGFR) loci is now well established. However, within the group of patients with craniosynostosis, there are several families and sporadic cases whose clinical features differ in variable degrees from the classically described syndromes of craniosynostosis. In this communication we present novel FGFR2 mutations associated with a spectrum of craniosyostosis phenotypes in 4 sporadic cases and in one family in which craniosynostosis segregates. The mutation and phenotype data presented emphasise the clinical variability of mutations at this locus and underline the plasticity of the phenotype-genotype relationship in this important group of congenital malformation syndromes. Mutations found were tyrosine 105 to cysteine, glycine 338 to glutamic acid, serine 351 to cysteine and glycine 384 to arginine. These are the first reported mutations in the first immunoglobulin-like loop (tyrosine 105 to cysteine) and the transmembrane domain (glycine 384 to arginine) of FGFR2, providing further insights into the mechanism of abnormal receptor function in FGFR2 mutations.