Apert syndrome (AS) is one of the most severe craniosynostoses and is characterized by premature fusion of craniofacial sutures. Mutations of either Ser252Trp or Pro253Arg in fibroblast growth factor receptor 2 (FGFR2) are responsible for nearly all known cases of AS. Here we show that mutant mice carrying the activation mutation, Ser252Trp [corrected] which corresponds to Ser252Trp in human FGFR2, have malformations mimicking the skull abnormalities found in AS patients. Mutant mice (Fgfr2(250/+)) are smaller in body size with brachycephaly and exhibit distorted skulls with widely spaced eyes. Unexpectedly, the premature closure of the coronal suture is accompanied by decreased, rather than increased, bone formation. We demonstrate that the Fgfr2-Ser252Trp [corrected] mutation does not cause obvious alterations in cell proliferation and differentiation; however, it results in increased Bax expression and apoptosis of osteogenic cells in mutant coronal suture. The accelerated cell death possibly reduces the space between osteogenic fronts of flat bones and results in the physical contact of these bones. Thus, our data reveal that dysregulated apoptosis plays an important role in the pathogenesis of AS related phenotypes.