BACKGROUND: The optimal management of high-grade spondylolisthesis in the growing child is controversial. Some authors have advocated for surgery in all cases regardless of symptoms. Surgical intervention results in a >10% risk of complications with increased risk of neurological injury associated with slip reduction maneuvers. There is a paucity of literature regarding nonoperative management in this setting. This study sought to obtain outcome measures in pediatric patients with high-grade spondylolisthesis managed either operatively or nonoperatively. METHODS: Database review was performed to identify patients with a high-grade (Meyerding grade III to V) spondylolisthesis managed either operatively or nonoperatively. Retrospective radiographic and chart review was performed. Patients were then contacted by phone to obtain current quality-of-life measurements using the Scoliosis Research Society (SRS)-30 questionnaire. RESULTS: Fifty-three patients were identified for inclusion in the study and 49 were contacted for 92% follow-up. Twenty-four patients were treated with operative intervention, and 25 patients were initially treated nonoperatively, but 10 went on to require surgical intervention. Mean age at presentation was 12.6 years (range, 8 to 17 y) and mean age at follow-up was 20.1 years (range, 10 to 29 y). There were no outcome differences between the groups. A more kyphotic slip angle was associated with worse SRS-30 outcome scores across all groups. In the nonoperative group, the slip angle was significantly larger in patients who failed conservative treatment (34 ± 17 degrees) than in those who remained nonsurgical at final follow-up (20 ± 14 degrees). Slip angle in the operative group was 27 ± 14 degrees. In surgical patients, an older age at surgery was associated with better SRS-30 outcome scores. CONCLUSIONS: Nonoperative management or "watchful waiting" of the minimally symptomatic or asymptomatic child with a high-grade spondylolisthesis is safe and does not lead to significant problems. Operative intervention for the symptomatic patient achieves similar long-term results compared with patients whose minimal symptoms do not warrant surgery. Delayed surgical intervention does not result in worse outcomes. Regardless of treatment modality, patients with a more kyphotic slip angle tend to have a poorer prognosis. LEVEL OF EVIDENCE: Level III.