Introduction Despite the advances in the surgical treatment of the EIA, the goals remain the same: stop the progression of the curve, correct the deformity, preserve coronal and sagittal balance, minimize surgical complications (adjacent kyphosis, adding adjacent segments, coronal, and sagittal imbalance); but mainly “preserve moving segments.” Currently, there is a common agreement to perform a selective fusion for curves Lenke 1 B; being not equal for curves Lenke 1 C. The objective of this work is the retrospective evaluation of clinical and radiographic results of the selective fusion in the AIS Lenke 1 curves, with B and C modifiers. Material and Methods From May 2007 until December 2010, a total of 25 patients with AIS Lenke 1 type with modifiers B and C were operated on by using selective thoracic fusion. All cases were operated in the Unit of spinal surgery of the Provincial Hospital of the Centenary. The average age at the time of surgery was 14.6 years. Overall, 23 were women and 2 were men (11.5:1). They were taken for this study, clinical and radiographic preoperative evaluations, also in the immediate postoperative period, and at the end of follow-up. The follow-up took place at the POP immediately, 2 months later, and at the first year. The degree of maturation was obtained by the Risser method, which was 3.7 preoperative (average of 2–4). Among the total number of selected patients, 12 had a lumbar modifier B and 13 had a lumbar modifier C. Results Thoracic postoperative Cobb 25.1, percentage of correction 59.51; lumbar postoperative Cobb 11.6, percentage of correction 72.38; thoracic Cobb at the follow-up 30.1, lumbar Cobb at the follow-up 12.4; plummet CSVL (global coronal balance) preoperative average 14 mm plummet CSVL (global coronal balance) immediate POP 9 mm plummet CSVL (global coronal balance) POP follow-up 10.3 mm, AVT thoracic preoperative 57 mm AVT thoracic postoperative immediate 22 mm, AVT thoracic postoperative to the follow-up 24 mm, AVT lumbar preoperative 45 mm, AVT lumbar postoperative immediate 19 mm, AVT lumbar postoperative to the follow-up 20 mm, sagittal thoracolumbar balance preoperative 6 mm (−16 to 15 mm), sagittal thoracolumbar balance postoperative 6 mm (−14 to 15 mm). Conclusion In spite of the fact that the majority of the articles in the literature belong to a grade IV of evidence, and not a few times the information is contradictory; the selective fusion of the thoracic spine in patients with AIS and Lenke pattern 1 with B and C modifiers, is a safe and effective technique to achieve an adequate correction of the deformity, preserving a greater amount of mobile lumbar segments. It is important to apply the criteria that are present in the current literature in a personalized way, adapting them to the characteristics and needs of each patient in particular, to optimize the results of this procedure. The strict control and full examination pre- and postsurgical of the patients that will be submitted to a selective instrumentation, must be accurate, to perform a correct indication and obtain the best clinical outcomes.