['It is unclear if psoas lengthening surgery is required in the treatment of patients with cerebral palsy (CP) with hip flexion deformity and previous studies show equivocal results with regard to functional outcome.', 'This study retrospectively assessed 12 patients with a diagnosis of spastic diplegia who underwent single event multilevel surgery in order to correct deformities in the sagittal plane distal to the hip. Both clinical and instrument gait analysis results were recorded preoperatively, at one year (short term) and at five years (mid term) postoperatively.', 'Clinically measured hip and knee movement improved at both short and mid term follow up. Correlations of clinically measured maximum hip and knee extension were significant at all three time points. Angles at terminal stance/toe off for hip and knee from kinematic data also showed significant correlations at all three time points.'] Does hip flexion deformity improve without psoas-lengthening after surgical correction of fixed knee flexion deformity in spastic diplegia?