We report a retrospective review of 62 consecutive patients who had a vascularised fibular transfer to reconstruct a large skeletal defect. We were particularly interested in the bone dynamics of the vascularised graft, since fractures occurred in 25% of the cases at an average time of eight months after surgery. Hypertrophy was more common when the limb was mechanically loaded; it was enhanced where the graft was not bypassed by internal fixation. The length of the graft and the use of additional bone graft material had no influence on the incidence of stress fracture or on hypertrophy. We conclude that a vascularised graft should be protected against fatigue fracture during the first year, and that a gradual increase in mechanical loading will enhance remodelling and hypertrophy.