The aim of the present study was to clinically and radiographically compare guided tissue regeneration (GTR) therapy with bioabsorbable polyglactin 910 barriers and conventional periodontal surgery in intrabony defects. In 26 patients with advanced periodontitis, 29 teeth exhibiting interproximal intrabony defects were treated; 15 by conventional periodontal surgery (control) and 14 by GTR (test). Before and 12 months after surgery, clinical parameters were assessed and standardized radiographs were taken. On the radiographs the distances from the cemento-enamel junction (CEJ) to the alveolar crest (AC), and the CEJ to the most apical extension of the bony defect (BD) were measured using a computer-assisted analyzing device (LMSRT). Twelve months after surgery, 24 patients with 27 lesions were available for examination. For both methods statistically significant (P < 0.001) probing depth (PD) reduction (mean ± standard deviation) of -4.49 ± 1.94 mm (n = 13, test) and -3.22 ± 1.48 mm (n = 14, control), as well as clinical attachment gain (CAL-V) of 3.41 ± 1.59 mm (test) and 2.07 ± 1.10 mm (control), was observed. Radiographic changes of the distance CEJ to AC of -0.95 ± 1.72 mm (n = 9, test), and -0.98 ± 1.53 mm (n = 11, control) were not significant. A significant bony fill (distance CEJ-BD) of 1.05 ± 1.22 mm was observed for the test group (P < 0.01); the 0.68 ± 2.04 mm bony gain for the control group was not statistically significant. The PD reduction (P < 0.05) and attachment gain (P < 0.01) in the test group was statistically significantly more favorable than in the control group. Twelve months after surgery, statistically more favorable PD reduction and attachment gain was observed using polyglactin 910 barriers than compared to conventional flap surgery. Hence, the use of bioabsorbable barriers for therapy of intrabony defects may be recommended. J Periodontol 1998; 69:1210–1217.