Objective: To evaluate the (cost-)effectiveness of a new patient-empowered follow up (FU) protocol in patients with Adolescent idiopathic Scoliosis (AIS) that is based on patient-reported outcome measures (PROMs), self-assessment tools and physical examination, which is compared to standard FU care by: 1) Effect evaluation, 2) Economic evaluation, 3) Implementation (process) evaluation. Study design: A multicentre pragmatic randomized trial design with two arms, combined with a patient preference cohort for each arm (partially randomized preference trial \[PRPT\]). Study population: A total of 812 AIS patients (age 10-18 years) treated by the Dutch AIS Consortium, representing the scoliosis treatment centres in the Netherlands, will be included. Three subgroups of AIS patients are distinguished, which are monitored over two years: 1. Pre-treatment group: adolescents with curve 10-25° (n=132 per arm; total n=264) 2. Post-brace treatment group (n=122 per arm; total n=244) 3. Post-surgery group (n=152 per arm; total n=304) Intervention: The new patient-empowered FU protocol (PE-FU) is based on PROMs, self-assessment tools and clinical assessment including physical examination. The protocol aims to detect curve progression or postoperative complications based on these patient-based and clinical parameters to substitute the need to obtain routine x-rays. X-rays will only be taken when progression or postoperative complications are suspected in the pre- and post-intervention groups based on predefined criteria. The standard FU protocol consists of routine full-spine radiographs and routine clinical evaluations.