This paper reports the use of real-time ultrasound methods to measure femoral anteversion (FAV), tibial torsion (TT), femoro-tibial rotation (FTR) at the knee and the summated rotational alignment (ΣRA = FAV+TT+FTR) in 537 healthy subjects age 5-18 years. The findings confirm knowledge that FAV decreases and lateral TT increases significantly with age in each of boys and girls. New findings relate to each of FTR (medial rotation of femur on tibia) and ΣRA. FTR, like TT, increases significantly with age in each of boys and girls. ERA changes significantly from being medially rotated in younger children to laterally rotated in older children with the cross-over from medial to lateral rotation occurring at 8-11 years of age; this explains the clinical observation that young children tend to in-toe as they walk and which resolves spontaneously with growth in most children. Overall, the data collected as means and standard deviations for each age and sex provide controls for comparison with data from subjects referred after school screening for scoliosis, having surgery for AIS and patients with patellofemoral pain syndrome which are considered elsewhere in this volume.