Purpose: To evaluate the efficacy of Emdogain versus placebo (its carrier) for the treatment of deep infrabony defects. Materials and methods: Thirty patients with an infrabony defect of at least 4 mm deep and at least 2 mm wide were randomly allocated for treatment with either Emdogain or placebo (the Emdogain carrier). The treating clinician was completely blinded to the therapy provided and performed all evaluations blindly up to the third year of follow-up. Outcome measures were tooth loss, complications, post-operative healing, patient's satisfaction with treatment and aesthetics, changes in probing attachment levels (PAL), probing pocket depths (PPD), gingival recessions (REC) and radiographic bone levels (RAD). Results: One year after treatment, both therapies had significantly improved clinical outcome measures: placebo group PAL gain = 3.3 mm, PPD reduction = 3.9 mm, and RAD gain = 2.5 mm; Emdogain group PAL gain = 3.4 mm, PPD reduction = 4.2 mm, and RAD gain = 2.5 mm. Both therapies induced statistically significant gingival recession (0.6 mm in the placebo and 0.8 mm in the Emdogain group). There were no statistically significant differences between groups for any of the outcomes tested. No teeth had to be extracted up to 3 years after treatment. Conclusions: There does not appear to be any clinical advantage when using Emdogain over its carrier (placebo) in the treatment of deep and wide infrabony defects. Keywords: Emdogain, infrabony defect, periodontitis, randomised controlled clinical trial