Background: Sparse objective data are available documenting changes of trochlear shape after trochleoplasty. Purpose/Hypothesis: The purpose was to investigate whether standardized magnetic resonance imaging (MRI) measurements that characterize trochlear dysplasia (TD) change significantly after arthroscopic deepening trochleoplasty (ADT) combined with medial patellofemoral ligament (MPFL) reconstruction. It was hypothesized that MRI measurements would approximate normal values. Study Design: Case series; Level of evidence, 4. Methods: Patients who underwent ADT between October 2014 and December 2017 were considered for this study. The preoperative inclusion criteria for ADT surgery were patellar instability, a dynamic patellar apprehension sign at 45° of flexion, a lateral trochlear inclination (LTI) angle of <11°, and failed physical therapy. MRI was performed pre- and postoperatively, and standardized MRI measurements were calculated: LTI angle, trochlear depth, trochlear facet asymmetry, cartilage thickness, and trochlear height. The Banff Patella Instability Instrument 2.0 (BPII) score, Knee injury and Osteoarthritis Outcome Score (KOOS), and Kujala score were obtained pre- and postoperatively. Results: A total of 16 knees in 15 patients (12 female and 3 male; median age, 20.9 years; range, 14.1-51.3 years) were evaluated. The mean follow-up time was 63.6 months (range, 23-97 months). The median LTI angle improved from 1.25° (range, –25.1° to 10.6°) preoperatively to 10.7° (range, –17.7° to 25.8°) postoperatively (P <.001), trochlear depth increased from 0.0 mm (range, –4.2 to 1.8 mm) to 3.23 mm (range, 0.25-5.3 mm) (P <.001), and trochlear facet asymmetry improved from 4.55% (range, 0.0%-28.6%) to 17.8% (range, 0.0%-55.6%) (P <.003). Cartilage thickness was unchanged: 4.5 mm (range, 1.9-7.4 mm) preoperatively and 4.9 mm (range, 0.6-8.3 mm) postoperatively (P =.796). BPII, KOOS, and Kujala scores improved significantly (P <.0034 for all). Conclusion: Combined ADT and MPFL reconstruction led to statistically significant and clinically relevant improvements in patient-reported outcomes and standardized MRI measurements that characterize TD. The improvements corresponded to those obtained by open trochleoplasty. No significant reduction in cartilage thickness was seen.