Based on four personal cases of osteogenesis imperfecta and dentinogenesis imperfecta, the authors review the semiological elements constituting the syndrome, and assign each case to the Sillence (1979) classification. The author established his classification on clinical criteria and the genetic nature of the various forms of osteogenesis imperfecta, however, the most recent discoveries concerning collagen biochemistry confirm that the condition is without doubt more heterogenous than suggested clinically, thereby better explaining the wide range of mutations encountered.