The aim of this study was to test whether bone could be formed in peri-implant defects at immediate transmucosal implants using guided bone regeneration. Ten patients (median age 48 years) underwent comprehensive dental care including the placement of an implant into an extraction socket immediately following removal of a tooth. An expanded polytetrafluoroethylene membrane and the mucoperiosteal flap were adapted around the neck of the implants, leaving the sites to heal in a transmucosal fashion. During implantation (baseline) and at membrane removal surgery 5 months later, the following clinical measurements from the implant shoulder were assessed at six sites: implant-bone contact (defect depth), level of the alveolar crest, level of the membrane, and distance from the crest to the implant body (defect width). Estimates of the defect volume bordered by the membrane, the implant, and the bony walls were calculated. At baseline, the mean defect depth was 4.7 mm (SD 1.3 mm, range 1 to 14 mm). At membrane removal, the mean defect depth had decreased to 2.1 mm (SD 0.8 mm). Compared to baseline, this decrease was statistically significant (P .01). The mean increase in bone height at the deepest defect site of each implant was 6.7 mm (SD 3.0 mm), which was significant (P .01). At baseline, the mean value for the defect volume estimates was 9.45 mm3 (SD 5.75 mm3). At membrane removal, a significant decrease (P .01) was found. After 5 months, 94% of the area beneath the membrane was filled with new bone. It was concluded that guided tissue regeneration at immediate transmucosal implants is successful in generating bone into peri-implant defects. Keywords: e-PTFE membrane, guided bone regeneration, implantation, new bone formation, transmucosal