The purpose of the present investigation was to describe the formation, maturation and eruption of the dentition, including supernumerary teeth in a sample of patients with cleidocranial dysplasia. The dentition was evaluated from orthopantomograms, intraoral radiographs, cephalometric films, surgically removed teeth and intraoral photographs in 19 patients (9 men, 10 women), aged 3.5 to 34 years. Formation of primary teeth was normal, whereas all patients but one had supernumerary permanent teeth. Frequency of supernumerary teeth ranged from 22% in the maxillary incisor region to 5% in the molar regions. Supernumerary teeth were formed lingually and occlusally to the normal teeth. Maturation of the primary dentition was normal, while permanent teeth were delayed from 1 to 4 yr. Supernumerary teeth were delayed about 4 years in relation to normal permanent teeth. Eruption of primary teeth was normal, whereas all patients had severe eruption problems of permanent teeth. It was hypothesized that the dental lamina for both primary and permanent dentition is normal, but does not resolve completely and therefore may form supernumerary teeth. Abnormalities of tooth morphology is related to inadequate space and arrested eruption. Delayed or arrested eruption is probably caused by diminished resorption of bone and of primary teeth and to the presence of multiple supernumerary teeth.