The clinical, radiographic and histologic findings are described in two cases of Ehlers Danlos Syndrome Type I with novel dental features. Defective dentinogenesis principally affecting the mandibular incisors result in aplasia or hypoplasia of root development predisposing to localized periodontal disease. A striking radiographic appearance with a bulbous enlargement of the roots together with pulp stones is seen in other teeth. 'Giant channels' and vascular inclusions resembling 'intermediate cementum' are prominent within this area. No evidence of Type III procollagen or collagen was detected with indirect immunofluorescence. It is suggested that an inherited collagen abnormality in a component common to dentin, skin, ligament and tendon probably explains both EDS I and the dentin dysplasia.