Background: Previous multi-center trials demonstrated the efficacy of a biodegradable chlorhexidine-gelatin chip (CHX) in reducing probing depth in patients with periodontitis. The present study utilized a subset from the parent study to determine if the CHX chip was effective in maintaining alveolar bone over a 9-month period. Methods: Forty-five subjects with at least four 5 to 8 mm pockets, stratified by smoking status, were enrolled in this double-blind controlled, placebo-controlled trial. Control groups received either placebo chip plus scaling and root planning (SRP) or SRP alone. Test group subjects received active CHX chip or SRP alone (to maintain the blind). Standardized radiographs were taken for quantitative digital subtraction radiography at baseline and 9 months. Results: At 9 months, 15% of SRP treated subjects experienced loss of bone in 1 or more sites, no subject treated with active chip plus SRP lost bone (P <0.01). At 9 months, significant differences in the change in probing depth and clinical attachment levels favoring the active chip over SRP alone or SRP plus CHX chip were also observed (P <0.05). Conclusions: These data indicate that the CHX chip, when used as an adjunct to scaling and root planing, significantly reduces loss of alveolar bone.