The purpose of this study was to retrospectively investigate changes in gait patterns after single-event multilevel surgery in children and adolescents with bilateral cerebral palsy. Three-dimensional instrumented pre- and postoperative gait data of 12 patients were compared to data of 12 healthy control subjects using principal component analysis to reduce the dimensionality of kinematic and kinetic gait data and detect gait differences. The differences between pre- and postoperative data and between postoperative data and data of control subjects were calculated using a linear mixed model. The results revealed 14 significant effects for pre- and postoperative waveforms and 11 significant effects for postoperative and control waveforms. Patients after single-event multilevel surgery walked with smaller internal foot progression angle throughout the gait cycle, lower knee flexion at initial swing, and earlier knee extension during terminal swing. Retained gait deviations included excessive pelvic tilt and internally rotated and flexed hips over the entire gait cycle. Contrary to our hypothesis, postoperative waveforms in the sagittal plane differed more from control waveforms than from preoperative waveforms. These results emphasize the importance of carefully planning further conservative therapy 2 years after single-event multilevel surgery.