BACKGROUND: Previous studies have shown inconsistent results on the association between diabetes mellitus (DM) and some clinical outcomes. We conducted a meta-analysis of observational studies to assess effect of DM on clinical outcomes after coronary stenting. METHODS: We searched for studies without language restriction in PubMed, Embase and Cochrane library prior to 2012. The clinical outcomes including in-stent restenosis (ISR), major adverse cardiac events (MACE), stent thrombosis (ST), target lesion revascularization (TLR) and target vessel revascularization (TVR). Adjusted odds ratio (OR), and the corresponding 95% confidence interval (95% CI) was summarized. RESULTS: 55 studies involving 128,084 total patients (38,416 DM patients and 89,668 controls) were eligible for our analysis. Overall, there were significant associations between DM and ISR (OR = 1.70, 95% CI: 1.53-1.89, I(2) = 0.0%), MACE (OR = 1.54, 95% CI: 1.36-1.73, I(2) = 29.0%), ST (OR = 2.01, 95% CI: 1.36-2.97, I(2) = 47.7%), TLR (OR = 1.46, 95% CI: 1.26-1.68, I(2) = 43.3%) as well as TVR (OR = 1.33, 95% CI: 1.17-1.51, I(2) = 48.3). Subgroup analysis showed that the associations were similar between BMS and DES implantation. Moreover, there was no significant association in the ST subgroup after 1-3 years follow-up. CONCLUSIONS: Our meta-analysis suggests that after coronary stent implantation, DM is associated with ISR, MACE, ST, TLR and TVR. DM appears to be a vital risk factor of these clinical outcomes.