Background: Angiotensin-Converting Enzyme Inhibitors (ACEIs) and Angiotensin Receptor Blockers (ARBs) are popular first-line agents for delaying the onset of diabetic nephropathy and diabetic kidney disease in diabetic patients without nephropathy and for reducing all causes of mortality in diabetic patients with nephropathy. However, long-term data showing a reduction in mortality from all causes or renal failure in type 2 diabetes patients with undetermined nephropathy taking ACEIs/ARBs are not available. Objective: To compare renal and other causes of death between those treated and not treated with ACEIs/ARBs in type 2 diabetes patients who are non-nephropathic, nephropathic and have an undetermined nephropathy status. Methods: Type 2 diabetes patients (n = 7,946) who registered with the Thailand Diabetes Registry Project (TDRP) in 2003 were followed-up prospectively for 5 years until January 25, 2008. Baseline demographic data and diabetic nephropathy status were recorded when the patient registered in the TDRP. Living statuses were retrieved from the database of each study site and causes of death were retrieved from the death certificates from the Bureau of Registration Administration of Thailand. Results: There were 716 type 2 diabetic patients that died within 5 years of registration in the TPDR from all causes of death. Of these cases, 66 died from renal causes. The mortality incidence from renal causes in undetermined nephropathy patients who were treated and not treated with ACEIs/ARBs was 1.25 and 1.30 per 1000 person-years, respectively. After controlling for the propensity score, the competing risk analysis showed that treatment with ACEIs/ ARBs was not significantly associated with prevention of death from renal or other causes in type 2 diabetes patients with an undetermined nephropathy status (HR = 0.83, 95% CI: 0.33-2.09, p-value = 0.688 for renal causes; HR = 1.26, 95% CI: 0.97-1.63, p-value = 0.085 for other causes). Treatment with ACEIs/ARBs was significantly associated with the prevention of renal and other causes of death in type 2 diabetes patients with nephropathy (HR = 0.49, 95% CI: 0.25- 0.95, p-value = 0.034 for renal causes; HR = 0.73, 95% CI: 0.56-0.95, p-value = 0.019 for other causes). Conclusions: Treatment with ACEIs or ARBs is not necessary for everyone, especially in type 2 diabetes patients with an undetermined nephropathy status. Healthcare services teams should screen for microalbuminuria before the treatment of all newly diagnosed type 2 diabetes patients with ACEIs or ARBs