Handedness was a more important factor in the amount of overgrowth following fractures of the femoral shaft in children in the present study than factors previously investigated. The lower limbs were measured and handedness was recorded in 112 children who had sustained their fractures fourteen to 101 months (mean, fifty-six months) before the study was undertaken. Fifty-two of these patients also had scanograms. The average overgrowth for all injured limbs was ten millimeters. The difference in the amount of overgrowth which was observed was this: when the fracture was on the same side as the dominant hand, the limb overgrew an average of eight millimeters, compared with fourteen millimeters when the fracture was on the side opposite the patient's dominant hand. This difference for the scanogram group was statistically significant (p less than 0.05). Overgrowth was significantly inhibited by overriding of fracture fragments and was enhanced by distraction. The age of the patient and the type and location of the fracture did not significantly affect overgrowth.