Background and aim: The most common form of periodontitis is chronic periodontitis, which is a destructive inflammatory disease of periodontal tissues and is usually associated with pocket formation, changes in density and height of alveolar bone, and sometimes gingival recession. Some patients are resistant to periodontitis treatment due to a weak immune system, smoking, and sometimes due to unknown reasons. Moreover, surgery is impossible in some cases; therefore, clinicians have to approach alternative methods such as laser therapy to achieve successful treatment outcomes. Since there are great differences among the results of previous clinical trials, a review study to investigate the materials and methods section of these studies seems necessary in order to find the reason of the controversies. The methodology of all the intervention studies that have evaluated the effect of diode laser on periodontitis treatment from 1997 to 2017 were examined and the results were reported. Conclusion: randomized controlled trials should comply with the correct protocol. All the details of the treatment protocol and severity of periodontitis should be recorded in order to achieve reliable results. It can be concluded that the results of some of the reviewed studies are not reliable.