Abstract Study Design Matched case-control study. Objective To find the amount of progression of deformity and its clinical consequences in the long term after implant removal (IR) as a result of late infection in adolescent idiopathic scoliosis (AIS). Background Summary Late IR is occasionally necessary after instrumented posterior correction of AIS because of late implant infection or implant-associated pain. The long-term outcome is not yet known because of the lack of studies with a comparable control group. Methods We observed 50 patients with AIS, who had pedicle screw instrumentation for posterior correction, for at least 10 years. Seven of these patients needed IR after 3.4 years (range, 1.1–7.9 years) years because of late implant-associated infection. We matched these patients with another 7 who had no complications (control), by curve type, Risser stage, age, and gender. We performed radiological measurements preoperatively, at 6 weeks, and 2, 5, and 10 years postoperatively. All patients completed the SRS-24 questionnaire at 2- and 10-year follow-up. Results Although the curve magnitude of the main thoracic curve was similar preoperatively (Cobb angle: IR, 57°±6°; control, 57°±10°) and corrected equally (IR, 18°±4°; control, 20°±7°) at 6 weeks, the deformity progressed in the IR group at 2 years (IR, 25°±11°; control, 17°±6°) and became statistically different at 10 years (IR, 31°±10°; control, 19°±6°; p<.05). There was no significant difference in total Scoliosis Research Society score between groups (IR, 99±13; control, 90±17; p>.05) at 10 years. Conclusions Late implant removal after posterior correction of thoracic AIS with pedicle screw instrumentation results in a loss of Cobb angle correction of about one third in coronal plane at 10-year follow-up, but without clinical relevance, as measured by the Scoliosis Research Society-24 questionnaire.