The effect of intra-uterine movement restriction on the development of motor functions was studied longitudinally by comparing infants born after uncomplicated breech position (n = 13) with control infants (vertex position, n = 5-10). Before birth, fetal leg posture was studied at regular intervals by means of real time ultrasound observations, and classified as complete (n = 1), inconsistent (n = 6), or incomplete (n = 6) breech position. Limited extension of the hips, preference posture and joint position in percentage of time (each until 12 weeks), withdrawal reflex and magnet response (until 26 weeks) and posture while sitting, standing and walking without support (up to 12-18 months) were assessed longitudinally. The results showed statistically significant, positive relationships between intra-uterine breech position and neonatal limited extension of the hip-joint, between limited extension of the hip-joint and the percentage of time that the hips are in flexion during the first 12 weeks, between this flexion of the hips (in percentage of time) and an abnormally 'flexed' walking pattern at 12-18 months, and finally, between a positive magnet response at 6 months and an abnormal walking pattern at 12-18 months. These findings suggest that intra-uterine movement restriction of the legs can cause long term alterations in the development of motor functions (leg posture, reflexes and posture while walking), possibly mediated by alterations in proprioceptive feedback mechanisms.