Background: Mutations in the FKBP10 gene were first described in patients with Osteogenesis imperfecta type III. Two follow up reports found FKBP10 mutations to be associated with Bruck syndrome type 1, a rare disorder characterized by congenital contractures and bone fragility. This raised the question if the patients in the first report indeed had isolated Osteogenesis imperfecta or if Bruck syndrome would have been the better diagnosis. Methods: The patients described here are affected by severe autosomal recessive Osteogenesis imperfecta without contractures. Results: Homozygosity mapping identified FKBP10 as a candidate gene, and sequencing revealed a base pair exchange that causes a C-terminal premature stop codon in this gene. Conclusions: Our study demonstrates that FKBP10 mutations not only cause Bruck syndrome or Osteogenesis imperfecta type III but can result in a severe type of isolated Osteogenesis imperfecta type IV with prenatal onset. Furthermore, it adds dentinogenesis imperfecta to the spectrum of clinical symptoms associated with FKBP10 mutations.