Background Polymyalgia rheumatica (PMR) and giant cell arteritis (GCA) are almost always treated with glucocorticoids (GCs), but long-term GC use is associated with diabetes mellitus (DM). The absolute incidence of this complication in this patient group remains unclear.Objective To quantify the absolute risk of GC-induced DMin PMR and GCA from published literature.Methods We identified literature from inception to February 2017 reporting diabetes following exposure tooral GC in patients with PMR and/or GCA without preexisting diabetes. A random-effects meta-analysis was performed to summarise the findings.Results 25 eligible publications were identified. In studiesof patients with GCA, mean cumulative GC dose was almost 1.5 times higher than in studies of PMR (8.2 gvs 5.6 g), with slightly longer treatment duration and longer duration of follow-up (6.4 years vs 4.4 years). The incidence proportion (cumulative incidence) of patients who developed new-onset DM was 6% (95% CI 3% to 9%)for PMR and 13% (95% CI 9% to 17%) for GCA. Based on UK data on incidence rate of DM in the general population,the expected background incidence rate of DM over 4.4years in patients with PMR and 6.4 years in patients with GCA (follow-up duration) would be 4.8% and 7.0%,respectively. Heterogeneity between studies was high(I2=79.1%), as there were differences in study designs,patient population, geographical locations and treatment.Little information on predictors of DM was found.Conclusion Our meta-analysis produced plausible estimates of DM incidence in patients with PMR and GCA,but there is insufficient published data to allow precise quantification of DM risk.