Study Design. Cross-sectional ultrastructural analysis of metallic debris as well as the tissue reaction surrounding spinal implants in patients with late operative site pain. Objective. To clarify the cause of late operative site pain by the ultrastructural analysis of the byproducts of metallic corrosion as well as the surrounding soft tissues. Summary of the Background Data. Late operative site pain has been identified as the most frequent cause of implant removal. Allergic reaction to metal as well as low-grade infection has been suggested as probable mechanisms. Methods. Fourteen spinal implants were removed because of late operative site pain. Tissues obtained from different zones surrounding these implants were analyzed by light microscopy, transmission electron microscopy, and scanning electron microscopy along with electron dispersion radiograph analysis. Results. No signs of infection were present. Either one of the 2 types of connective tissue (dense or loose) were found to surround the implants. Macrophage counts were most abundant in zone II (around pedicular screws) when compared to other zones (zone I: around the rods; zone III: around the transverse rod connectors). In contrast, particulate debris was more abundant and larger in size in specimens from zone III. Two types of metallic debris were identified. The rusty appearing particles contained mostly iron (Fe), whereas the black appearing particles were rich in chromium (Cr). Conclusion. This study produced useful information regarding the production and distribution of particulate metallic debris around stainless steel spinal implants.