At least three different implant pockets for transaxillary submuscular (TASM) augmentation mammaplasty have been reported in the literature. To verify and clarify the features of the anatomical structures involved in a TASM procedure the authors studied the anatomy of the anterior thorax in operated and unoperated breasts of ten fresh female cadavers. In particular, some fascial and muscular observations are stressed, demonstrating that TASM augmentation mammaplasty always leads to a pocket where the upper one-third of the prosthesis is covered by the pectoralis major muscle, while the inferior two-thirds lies in a subglandular/subcutaneous plane.