Objective: To evaluate the efficacy of oily calcium hydroxide suspension (OCHS) in the of treatment of infrabony defects. Method and Materials: Thirty patients with advanced chronic periodontitis, with one deep infrabony defect, were randomly treated with open flap debridement (OFD) (control) or OFD + OCHS (test). Clinical measurements were performed at baseline and 9 months after treatment. Surgical reentry was performed after 9 months. The primary outcome variables were reduction in probing pocket depth (PPD) and gain in relative attachment level (RAL). The secondary outcome was the reduction in depth of defect (DOD) measured intrasurgically. Results: A statistically significant reduction in PPD was observed at the end of 9 months, with the control group showing a mean reduction of 2.06 ± 0.59 mm from baseline to 9 months and the test 1.06 ± 1.22 mm (P >= .05). There was no statistically significant gain in RAL at the end of 9 months, with a mean of 0.60 ± 0.50 mm in the control group and 0.60 ± 0.91 mm in the test (P >= .05). No statistically significant difference was observed in DOD at 9 months, with a mean difference of 0.80 ± 0.77 mm in the control group and 0.66 ± 0.97 mm in the test (P >= .05). Conclusion: Within the limitations of the study, OCHS failed to demonstrate any superior clinical outcomes in comparison with OFD. Schlagwörter: infrabony defects, oily calcium hydroxide suspension, open flap debridement