An odd complication following routine breast augmentations was observed in two patients. Single-lumen. textured, high-profile, saline-filled mammary implants were placed in the submuscular plane and postoperative course was uneventful in the presented cases. Unilateral, gradual. and spontaneous swelling in one of the operated breasts was observed 6-14 months after surgery that prompted patients for examination. MRI showed regular external contours of the mammary implants without any evidence of rupture or extracapsular leakage. However, a Substantially volumetric increase in the auto-inflated implant was noted since transverse diameter of the right breast implant was twice the left normal implant. All cases had to be re-operated and implants were explanted. Auto-inflated implants were checked and were found to be intact. Intraoperative findings included swelling of the implant and brown discoloration of the previously-transparent saline solution. Furthermore, composition of the fluid inside the expanded implant was found to have changed, possibly through an osmotic gradient.