BACKGROUND Periprosthetic capsules are a common reaction of the body to silicone or polyurethane breast implants. The aim of this study was to evaluate similarities and differences in the histological features of periprosthetic capsules surrounding silicone implants and polyurethane foam-coated implants and to correlate those features with the age of the implants. METHODS Tissues were studied from 41 periprosthetic capsules surrounding textured prostheses and from 20 capsules surrounding polyurethane foam-coated implants. For each sample we evaluated synovial metaplasia, density of collagen fibers or fibrosis, orientation of collagen fibers, and foreign body reaction (granulomatous reaction). RESULTS Synovial metaplasia was seen in the capsular tissue from both types of implant, but more so from capsules surrounding polyurethane implants more than 5 years old. The density and orientation of the collagen fibers and the foreign body reaction were very similar for the two types of implant.