Study Design. A single-center, retrospective study of 39 consecutive patients with Lenke 5 adolescent idiopathic scoliosis (AIS), all operated by a single surgeon using identical surgical technique and type of instrumentation (pedicle screws). Objective. The objective of this study is to evaluate the effect of implant density on coronal and sagittal correction in the treatment of Lenke 5 AIS. Summary of Background Data. There is an increasing trend in the use of pedicle screws in spinal corrective surgery. It is reported that decreased numbers of pedicle screws (low screw density) have no effects on the clinical outcomes for patients with Lenke 1 AIS. However, no previous studies have investigated the effects of reduced density of screw implantation on coronal correction and sagittal lumbar lordosis in patients with Lenke 5 AIS. Methods. Thirty-nine consecutive patients with Lenke 5 AIS underwent single-stage posterior correction and instrumented spinal fusion with pedicle screw fixation between 2006 and 2010. The radiographs were analyzed before surgery, immediately after surgery, and at the 2-year follow-up. General information of patients was recorded. Pearson correlation analysis was used to analyze the correlation between implant density, coronal Cobb angle correction, and correction index (postoperative correction/preoperative curve flexibility). The relations between implant density and magnitude of coronal and sagittal curve correction were also investigated. Results. The mean patient age at the time of operation was 14.5 years. The mean preoperative lumbar curve of 48.5° ± 9.2° was corrected to 13.7° ± 7.2° (72% correction) at a 2-year follow-up. There was a significant correlation between implant density and curve correction (r = 0.43, P < 0.05). No correlation was detected between implant density and correction index (r = −0.21, P = 0.20), and there was also no correlation between implant density and magnitude of sagittal curve correction (r = 0.065, P = 0.693). Conclusion. Without curve flexibility taken into consideration, implant density is positively correlated with thoracolumbar or lumbar coronal Cobb curve correction. No significant correlation is found between screw density and correction index, if the effect of the flexibility was eliminated. There was no association between implant density and magnitude of sagittal curve correction before and after surgery.