Despite being the commonest inherited disease of bone, osteogenesis imperfecta (OI) is a rare cause of fractures in daily clinical practice. Its prevalence in the general population is 1 to 5 per 100 000. The clinical spectrum ranges from mild forms with relatively few fractures and normal mobility to the lethal form, with multiple intrauterine fractures and death in perinatal period. The diagnosis of OI is based on fracture rates, family history, and clinical signs. However, the rarity of the condition coupled with the subtle signs of mild OI can lead to cases being missed altogether or misdiagnosed in some as “post-menopausal” osteoporosis. In asymptomatic members of a family with mild OI, it is even harder to decide whether they have the condition or not. It has recently been suggested that consultation by a physician familiar with the variability of OI (such as a medical geneticist) is essential for the early diagnosis.1 Clearly, this is possible only in selected centres of expertise, and in most clinical settings one is forced to tackle the problem with locally available resources. A 30 year old lady with known OI presented to the “Bone Clinic” with her two children in February 1992. The diagnosis of OI in the family was established three years before this visit when her 3 year old daughter was brought to the local accident and emergency department for a skull fracture with minor trauma. This child had suffered two long bone fractures previously, also with minor trauma. This led to initial suspicion for “non-accidental injury” or child abuse, though the family history suggested otherwise. The child's 65 year old grandmother had a history of four fractures, fracture of both “legs” (details unclear) at age 6 months, fracture of a bone in left foot age 16 and a fractured right forth …