The Ilizarov method of lengthening was used to correct deformities of the lower extremity in six patients who had type-I osteogenesis imperfecta, as categorized by Sillence et al. The average age was thirty-one years (range, fourteen to fifty-one years). The deformities included shortening of four tibiae and three femora as well as an angular malalignment (average, 28 degrees; range, 20 to 40 degrees) of all four tibiae and one femur. One patient also had a non-union of the right femur.The average angular correction was 23 degrees (range, 20 to 30 degrees). The seven limb segments gained an average of 6.6 centimeters (range, two to eleven centimeters) in length. All limb-length discrepancies were corrected to within two centimeters of the length of the contralateral limb. At an average of three years and four months (range, one year and seven months to six years), the roentgenographic appearance of the fully matured bone was comparable with that of the original bone. There were no fractures or increases in the angulation of the segment of new bone. Two patients had pain when walking: it was related to a chronic pin-track infection in one and to osteoarthrosis of the ankle in the other. The functional status of four patients was improved and that of the other two patients was unchanged. All six patients were pleased with the outcome of the procedure.There were eighteen complications: stiffness of the knee in two patients; a peroneal nerve palsy in two; a superficial pin-track infection in three; and a deep pin-track infection, greater-than-normal loss of blood intraoperatively, loosening of two pins, worsening of the instability of the knee, and an infection in the knee in one patient each. In another patient, a Rush rod that had been placed before correction of the deformity migrated proximally and had to be removed after completion of the correction. There were five fractures.