This study evaluated knee hyperextension course in children with cerebral palsy over a 5-year follow-up. Knee hyperextension was identified in 308 knees, of which 97 had follow-up greater than 5 years. Between the tests, 40% of limbs had plantar flexor lengthening (PFL). Overall, knee flexion and ankle dorsiflexion in stance increased (P<0.0001). Similar changes were noted between limbs that had PFL and those that did not. PFL is indicated in cases associated with equinus. However, the role of multilevel surgery in the treatment of knee hyperextension needs to be further determined.