The rare hereditary disease, dentinogenesis imperfecta, is a disturbance of dentin formation in both the deciduous and permanent dentitions. It may be associated with osteogenesis imperfecta, though it is probably that the two diseases are carried by different genes. This association was recognized in a 19-year-old man. Dentinogenesis imperfecta had been diagnosed at the age of 6 and had been regarded as a mutation; 11 years later, an atypical form of osteogenesis imperfecta developed. The case is atypical because of the apparent absence of dentinogenesis imperfecta in the patient's family. The dental manifestations may have heralded the bone disease.