" Assessment of the ambulatory patient who has cerebral palsy (CP) involves serial evaluations by orthopaedic surgeons, neurosurgeons, rehabilitation specialists, and therapists as well as 3-dimensional gait analysis (3DGA). The most common subtype of CP in ambulatory patients is diplegia, and the most common severity is Gross Motor Function Classification System (GMFCS) Levels I, II, and III. " Increased tone in the skeletal muscle of patients with CP can be managed with focal or generalized, reversible or irreversible means. One method of irreversible tone control in spastic diplegia is selective dorsal rhizotomy. A careful preoperative assessment by a multidisciplinary team guides a patient's tone-management strategy. " Abnormal muscle forces result in abnormal skeletal development. Resultant lever-arm dysfunction of the lower extremities creates gait abnormality. A comprehensive assessment of gait is performed with 3DGA, supplementing the clinical and radiographic examinations for surgical decision-making. " Single-event multilevel surgery (SEMLS) involves simultaneous correction of all musculoskeletal deformities of the lower extremities in a single setting. Specialized centers with attendant facilities and expertise are necessary. SEMLS often follows years of medical treatment, therapy, and planning. Some procedures can be performed with the patient in the prone position for technical ease and optimal assessment of transverse-plane alignment. " Objective gains in patient function are made until 1 to 2 years after SEMLS. Most ambulatory children with diplegia undergoing SEMLS maintain function at their preoperative GMFCS level but can make quantifiable improvements in walking speed, oxygen consumption, gait quality, and patient-reported functioning. .