BACKGROUND AND OBJECTIVES: Although low-level laser therapy (LLLT) has been demonstrated to have a biomodulatory effect on periodontal tissue, no systematic review has exclusively addressed its effectiveness as an adjunct to non-surgical periodontal treatment. This study aimed to evaluate whether an additional benefit exists for the application of LLLT compared with scaling and root planing (SRP) alone. MATERIAL AND METHODS: An extensive search was conducted in the Cochrane Library (Issue 8, 2015), PubMed (1997) and EMBASE (1947) before August 2015 for randomized controlled trials (RCTs). The bias risk was assessed with the Cochrane tool for risk of bias evaluation. A meta-analysis was performed using REVMAN 5.3. RESULTS: After independent screening of 354 initial records, eight publications (seven RCTs) were included. However, six were rated as 'having a high risk of bias' as a result of major methodological weakness in 'allocation concealment' and 'blinding of key personnel'. Meta-analysis showed that LLLT-mediated SRP demonstrated significant short-term benefits over SRP monotherapy in the improvement of the probing pocket depth (p = 0.0009 at 1 mo; p = 0.03 at 2 mo) and the level of interleukin-1β in the gingival crevicular fluid (p = 0.01 at 1 mo). Nevertheless, LLLT failed to show significant additional intermediate-term (3 and 6 mo) effects in terms of clinical parameters and alveolar bone density. CONCLUSION: These findings indicated that LLLT showed only short-term additional benefits after conventional SRP. Its long-term effects remain unclear due to substantial methodological weaknesses and an insufficient number of current studies. Future RCTs with better designs and longer follow-up periods are required to assess the effectiveness of LLLT as an adjunctive treatment strategy in patients with periodontal disease.