A series of investigations was undertaken to evaluate the extent and predictability of periodontal regeneration with barrier membranes in deep infrabony defects. This study reports the clinical outcomes in terms of probing attachment level (PAL) gains, probing pocket depth (PPD) reduction, and recession (REC) of marginal gingiva. Forty deep 1, 2, and 3-wall combination infrabony defects treated with membranes were evaluated 1 year postoperatively following a strict plaque control regimen (mean plaque score = 6.1%, bleeding score = 4% at 1 year). A PAL gain of 6.1 +/- 2.5 mm along with a PPD reduction of 5.9 +/- 2.5 mm were observed. A PAL gain of 2 mm or more was detected in almost 90% of the treated sites. No site lost attachment. Residual PPD was 3 mm or shallower in 95% of the sites. It is concluded that treatment of deep infrabony defects according to the principles of guided tissue regeneration and a strict plaque control regimen represents an efficacious and predictable treatment alternative.