Successful removal of long-term implanted plombage sponge, its chemical analysis and changes in its mechanical characteristics are reported. A 52-year-old woman who had undergone an intrapleural sponge plombage operation because of tuberculosis, and had since shown an uneventful medical history for 35 years, was referred with a complaint of back skin induration over the previous surgical scar. Resection of the implanted sponge was performed. The ribs attached to the sponge were atrophic and had fused with each other. The sponge had invaded the 6th rib and formed a window-like defect in the fused bony ribcage. The skin induration was found to be caused by hematoma due to damage of the intercostal artery by the sponge. In the sponge, which was made from polyvinylformal, connective tissue infiltration was observed to a depth of 5 mm. The innermost part of the sponge was free from connective tissue infiltration, but the sponge had lost its initial elasticity.