Context The effect of periodontal therapy on diabetes outcomes has not been established. Objective This update examines the effect of periodontal treatment on diabetes outcomes. Data sources Literature since October 2009 using MEDLINE. Study eligibility criteria Published RCTs including periodontal therapy for diabetic subjects, a metabolic outcome, an untreated control group, and follow-up of 3 months. Data extraction Pre-defined data fields, including study quality indicators were used. Data synthesis A search revealed 56 publications of which 9 met inclusion criteria. Mean change of HbA1c from baseline was compared across treatment groups. Pooled analysis was based on random effects models. Results A meta-analysis indicated a mean treatment effect of −0.36% HbA1c (CI −0.54, −0.19) compared to no treatment after periodontal therapy (p < 0.0001). Heterogeneity tests revealed only minimal evidence of publication bias (I2 = 9%). Limitations Small sample size and high risk of bias remain problematic for studies of this type. Periodontal therapy varied considerably. Conclusion The modest reduction in HbA1c observed as a result of periodontal therapy in subjects with type 2 diabetes is consistent with previous systematic reviews. Despite this finding, there is limited confidence in the conclusion due to a lack of multi-centre trials of sufficient sample size are lacking.