Dentinal Dysplasia Type I is a rare condition affecting the deciduous and permanent dentitions, in which the teeth present with short roots and considerably reduced or obliterated pulp spaces. These features were observed on the radiographs of a patient referred for orthodontic assessment, and an investigation of other members of the family revealed that the father and two siblings were also affected. There were variations in the lengths of the roots in those affected, and thus a subclassification of the dysplasia is proposed.