An unintended retained foreign object after primary breast augmentation is very uncommon, and there is not a reliable breast-augmentation-specific percentage that applies to every practice. A breast implant itself is, technically, a medical implant or foreign material, but an RFO usually means something unintentionally left behind, such as a sponge, instrument fragment, or needle fragment. Modern operating room counts, checklists, and accredited facility protocols are designed to make this event rare. If you are asking because of symptoms or an imaging finding, bring the concern directly to your surgeon rather than trying to estimate risk from statistics. Persistent focal pain, a palpable hard object, recurrent swelling, drainage, infection, or an unexpected X-ray, mammogram, ultrasound, or MRI finding should be evaluated. The right imaging test depends on the exam and on what material is suspected.