Three features of cleidocranial dysplasia that are not always appreciated are hypoplastic iliac wings, short stature, and brachydactyly. Because of the pelvic abnormality, pregnant women may require a cesarean delivery. Short stature and brachydactyly indicate more generalized skeletal abnormalities. These are derived from endochondral and intramembranous ossification, but the distinction between these 2 processes is oversimplified because both processes are involved in long bone and clavicular development. Two sections follow: the biology of RUNX2 and the nature of haploinsufficiency in RUNX2 mutations for cleidocranial dysplasia.