We report the case of a young boy who had had multiple bone fractures (more than 10) since the age of 19 months. The father had the same clinical history. The clinical examination was normal for his age except blue sclera. The bone densitometry showed a severe osteoporosis for his age. Biological exam swere correct. The genetic exploration revealed mutation of COL1A2 gene. With this clinical history, the diagnosis of Osteogenesis imperfecta (OI) was retained. OI is a hereditary dystrophy with abnormal synthesis or metabolism of collagen with, often, mutation of COL1A1 or COL1A2 genes. There are 7 different forms. We consider the possible differential diagnoses. The goal of any treatment is to promote bone remineralisation and to decrease the fracture frequency. The treatment includes calcium and vitamin D, and in the presence of some precise criteria, biphosphonate therapy.