Hereditary dentin defects are divided into dentinogenesis imperfecta and dentin dysplasia. We identified a family segregating severe dentinogenesis imperfecta. The kindred spanned four generations and showed an autosomal-dominant pattern of inheritance. The proband was a child presenting with a severely affected primary dentition, with wide-open pulp chambers and multiple pulp exposures, resembling a DGI type III (DGI-III) pattern. We hypothesized that a mutation in the DSPP gene is responsible for this severe phenotype. Mutational analyses revealed a novel mutation (c.53T>A, p.V18D) near the intron-exon boundary in the third exon of the DSPP gene. We analyzed the effect of the mutation by means of an in vitro splicing assay, which revealed that the mutation did not affect pre-mRNA splicing. Further studies are needed for a better understanding of the nature of the disease and the development of an appropriate treatment strategy.