Background: FFR of deferred PCI lesions can predict future cardiovascular events. However, the prognostic utility of FFR remains unclear in diabetic patients in view of the potential impact of the diffuse nature of vascular disease process. We aimed to study the relation between fractional flow reserve (FFR) values and long-term outcomes of diabetic and non-diabetic patients with deferred percutaneous coronary intervention (PCI). Methods: Patients with FFR assessment and deferred PCI (n=630) were enrolled and stratified according to diabetes mellitus (DM) status and FFR values. Patients were followed over a median of 39 months. Cox proportional hazard regression models were used to analyze the association between clinical endpoints and clinical factors such as DM and FFR. Results: In non-diabetics (n=450), higher FFR values were associated with less cardiovascular events (hazard ratio (HR) for death and myocardial infarction (MI) [95% confidence interval (CI)], 0.61[0.44 to 0.86] per 0.1 increase in FFR, p=0.007; HR for revascularization [95% CI], 0.66[0.49 to 0.9] per 0.1 increase in FFR, p= 0.006). In diabetics (n = 180), there was no difference in death and MI across the range of FFR values. Among those patients with an FFR >0.85, diabetics had a more than two-fold higher risk of death and MI than non-diabetics (HR [95% CI], 2.20 [1.19 to 4.01], p = 0.015). Conclusion: Among non-diabetic patients with deferred PCI, a higher FFR was associated with lower rates of death, MI and revascularization. On the contrary in diabetic patients with deferred revascularization, FFR was not able to differentiate the risk of cardiovascular events. (C) 2016 Elsevier Ireland Ltd. All rights reserved.