Purpose: To evaluate the clinical efficacy of photodynamic therapy (PDT) adjunctive to scaling and root planing (SRP) in patients with untreated chronic periodontitis based on up-to-date evidence. Methods: MEDLINE and the Cochrane Library were systematically searched to identify eligible randomized controlled trials (RCTs), supplemented by a manual literature search. Mean differences (MD) and the corresponding 95% confidence intervals (CI) of probing depth (PD) reduction and clinical attachment level (CAL) gain were synthesized. The I-2 test and Q statistics were used to determine the inter-study heterogeneity. Subgroup analysis based on smoking status was performed. Results: Eleven RCTs with a total of 243 subjects were included. Significant improvement in PD reduction (MD = 0.13, CI:0.02-0.24, p = 0.02) and marginal significant improvement in CAL gain (MD = 0.18, CI: -0.005-0.363, p = 0.056) were observed in favor of SRP+PDT at 3 months. When evaluated at 6 months after baseline, the association of PDT with SRP resulted in a significant benefit in PD reduction (MD = 0.40, CI:0.05-0.74, p = 0.03), but not in CAL gain (MD = 0.37, CI: -0.18-0.93, p = 0.18). Subgroup analysis revealed that the combined therapy produced no significant improvements in PD and CAL at neither 3 months nor 6 months for studies with smokers. No treatment-related adverse events or side effects had been reported by the included studies. Conclusions: Pooled analysis suggests a short-term benefit of PDT as an adjunct to SRP in clinical outcome variables. However, evidence regarding its long-term efficacy is still insufficient and no significant effect has been confirmed in terms of CAL gain at 6 months. Future clinical trials of high methodological quality are needed to establish the optimal combination of photosensitizer and laser configuration. (C) 2017 Elsevier B.V. All rights reserved.