BACKGROUND: Position of the nipple-areolar complex (NAC) is an important factor in the esthetic impression of the breast, and NAC malposition is often an issue in breast reconstruction after nipple-sparing mastectomy (NSM). The purpose of this study was to evaluate the degree of NAC malposition depending on several factors using data quantified with the Mamma Balance application (Medic Engineering K.K., Kyoto, Japan). METHODS: Patients who underwent unilateral breast reconstruction after NSM at eight hospitals in Japan between 2007 and 2020 were retrospectively investigated. Using Mamma Balance, NAC malposition was quantified separately in horizontal and vertical directions using patient photographs from pre-operatively and 6-24 months post-operatively. The degree of malpositioning was then statistically compared using various factors. RESULTS: The NAC deviated more cranially and medially with implants than that with flaps. Cases with latissimus dorsi flap showed lateral malposition more often than cases with deep inferior epigastric artery perforator flap. With flaps, lateral incisions showed more lateral malposition, and peri-areolar incisions tended to show more medial NAC malposition. In cases with severe post-operative infection of the implant, the NAC tended to deviate cranially. In radiation cases, the NAC deviated cranially. No significant difference was observed according to the degree of breast ptosis or use of the pull-down operation. Only a very weak correlation was observed between a larger amount of mastectomy and more cranial NAC malposition with both flaps and implants. CONCLUSIONS: This study provides insights into the tendencies and characteristics of NAC malposition.