OBJECTIVE Significant investigation in the adult population has generated a body of research regarding proximal junctional kyphosis (PJK) and proximal junctional failure (PJF) following long fusions to the sacrum and pelvis. However, much less is known regarding early complications, including PJK and PJF, in the ambulatory pediatric patient. As such, the objective of this study was to address the minimal literature on early complications after ambulatory pediatric patients underwent fusion to the sacrum with instrumentation to the pelvis in the era of sacral-alar-iliac (S2AI) instrumentation. METHODS The authors performed a retrospective review of pediatric patients with nonidiopathic spinal deformity < 18 years of age with ambulatory capacity who underwent fusion to the pelvis at a multisurgeon pediatric academic spine practice from 2016 to 2018. All surgeries were posterior-only approaches with S2AI screws as the primary technique for sacropelvic fixation. Descriptive, outcome, and radiographic data were obtained. The definition of PJF included symptomatic PJK presenting as fracture, screw pullout, or disruption of the posterior osseoligamentous complex. RESULTS Twenty-five patients were included in this study. Nine patients (36.0%) had 15 complications for an overall complication rate of 60.0%. Unplanned return to the operating room occurred 8 times in 6 patients (24.0%). Four patients (16.0%) had wound issues (3 with deep wound infection and 1 with wound breakdown) requiring reoperation. Three patients (12.0%) had PJF, all requiring reoperation. A 16-year-old female patient with syndromic scoliosis underwent extension of fusion due to posterior tension band failure at 6 months. A 17-year-old male patient with neuromuscular scoliosis underwent extension of fusion due to proximal screw pullout at 5 months. A 10-year-old female patient with congenital scoliosis underwent extension for PJF at 5 months following posterior tension band failure. One patient had pseudarthrosis requiring reoperation 20 months postoperatively. CONCLUSIONS Fixation to the pelvis enables significant deformity correction, but with rather high rates of complications and unexpected returns to the operating room. Considerations of sagittal plane dynamics for PJK and PJF should be strongly analyzed when performing fixation to the pelvis in ambulatory pediatric patients.