Hemimandibular hyperplasia is a rare type of condylar hyperplasia which leads to facial asymmetry. Its surgical correction may be challenging since it usually requires complex mandibular osteotomies. Mandibular inferior border ostectomy is poorly described in the literature. The aim of this report is to present a new surgical technique guided by a customized surgical splint manufactured using computer-aided design/computer-aided manufacturing technology. Very good aesthetic results are achieved as it is very precise.