The purpose of this study was to assess growth patterns after lengthening of the congenitally short femur or tibia in children younger than 6 years. Twenty such children underwent 28 bone segment lengthenings (13 femora and 15 tibiae) by distraction osteogenesis. Our results show that femoral lengthening in children younger than 6 years does not lead to growth inhibition, whereas isolated femoral lengthening may be associated with growth stimulation. Isolated tibial lengthening in children younger than 6 years does not lead to growth inhibition, whereas simultaneous femoral and tibial lengthening or two tibial lengthenings in close succession can lead to tibial growth inhibition.