The author of this paper asses lower extremity in 141 children with osteogenesis imperfecta, treated in University Children Hospital in Krakow in years 1988-2002: number of fractures, presence of the deformation, radiological findings, possibility of walking. Only 3 from this group did not suffer from lower extremity long bone fractures. In remaining patients, the number of fractures was 4 on average with type I and IV, and 46 fractures in children with type III osteogenesis imperfecta in each patient. Perinatal fractures appeared in 26 children with type II or III oi. In remaining, first fracture happened at the age of 23 months on average. 21% of the children had never walked before, and the rest of them started pionisation at the age of 20 months on average. Lower extremities deformations appeared in 113 children (80%). We assessed typical deformity pattern, based on clinical and radiological findings: varisation of femur and antecurvation of the tibia. The movement limitations in hips or knees was found in 29 children. Radiological changes in growth cartilage, so-called "popcorn calcification" were found in 15 children with type III of osteogenesis imperfecta.