BACKGROUND: Recent studies have provided diverging results regarding the factors that may affect sensibility after primary breast augmentation. Implant volume is believed to be an important factor, but the relation of implant size to breast volume has not been adequately addressed. In addition, the literature shows that a conflict exists when the periareolar and inframammary approaches are compared. This study aimed to refine the volumetric analysis comparing the implant and final breast size as well as the intrinsic association of these two factors with postoperative sensory alteration of the breast. METHODS: A prospective study investigated patients who underwent aesthetic breast augmentation between June 2004 and October 2005 (i.e., a 16-month period) at the Ivo Pitanguy Institute. The sensibility in nine regions of the breast was tested before and after surgery using Semmes-Weinstein monofilaments. Breast sizers were used to compare the pre- and postoperative breast volumes. Statistical analysis of the data took into consideration the relative volume of the implant, the surgical approach, the presence of minor complications, the breast-feeding history, and the subjective evaluation of sensory changes in the patients. RESULTS: A total of 37 patients who underwent breast augmentation were examined preoperatively. The relative volume of the implant was found to be associated with sensibility alterations. No difference was found between the periareolar and inframammary incision approaches. Other factors such as previous breast-feeding, minor complications, and subjective alterations were not associated with sensory alterations. CONCLUSIONS: The study findings suggest that larger implants and smaller breasts show an increased association with postoperative sensory alterations of the breast. Plastic surgeons and their patients should be aware of this possibility. Implant volume should be considered together with breast size to avoid sensory complications, and this is summarized in the concept of relative volume.