Background Many studies have been dedicated toward bettering the understanding of the anatomy of this branch and the relative danger zone. However, most of these articles have focused on identifying the location of this branch based on its trajectory and associations with deep structures, causing some difficulties for aesthetic surgeons to identify its location during facial aesthetic surgery. Here, we present the concept of the marginal nerve triangle; its contents, relations and clinical applications in cosmetic surgery are discussed. Methods This is an anatomical study performed using 64 hemifaces from 32 Peruvian fresh cadavers (25 men and 7 women). They were dissected manually and observed macroscopically by the authors. The marginal nerve and the related structures were dissected from its origin to the terminal branches and associated with the described triangular area. Results The marginal branch of the facial nerve was found to lie in the described triangle in all cases. This is a triangular area formed by the intersection of three points located at the lateral commissure of the mouth, the mastoid apophysis and a point located over the anterior border of the extracellular matrix (ECM) muscle with a line which intersects the lateral commissure of the mouth and the mandibular groove. Conclusions The trajectory of the marginal and cervical branches of the facial nerve can be reliably and easily found at the described triangle following the reference points. This study will help guide surgeons to these branches of the facial nerve as it applies to aesthetic surgery.