The purpose of the present investigation was to describe the size, shape, and morphologic characteristics of the cranial base in adult patients with cleidocranial dysostosis in an attempt to contribute to an improved understanding of the syndrome. The sample comprised seventeen patients with cleidocranial dysostosis, eight males and nine females aged 16 to 46 years. The morphology was evaluated from lateral cephalometric radiographs and midsagittal tomograms of the cranial base. The size of the anterior and posterior cranial base and the cranial base angle were compared to normative data. In addition, a qualitative screening for abnormal morphologic traits in the cranial base was carried out. The anterior and posterior cranial base was significantly shorter and the cranial base angle smaller in the syndrome groups than in the control groups. Patients with cleidocranial dysostosis exhibited high frequencies of anomalous traits in the cranial base, the most striking being a distortion of the clivus. In 82 percent the clivus was flexed, with the convexity toward the endocranium. All patients exhibited bulbous dorsum sellae, and 47 percent had small pituitary fossae. It is suggested that bone remodeling showed less resorption than normal in the craniofacial region of patients with cleidocranial dysostosis.