Objective: To evaluate the relationship between micro-albuminuria (MA) and the presence and extent of coronary artery disease (CAD). Methods: Four hundred and two consecutive patients were divided into 4 groups based on the presence of diabetes mellitus (DM) and MA: DM(+)/MA(+), DM(+)/MA(-), DM(-)/MA(+), and DM(-)/MA(-). Severity of CAD was assessed by the Gensini scoring system. Results: The Gensini score was 57 +/- 38.2 vs 16.5 +/- 19.5 (P < .001) in the DM(+)/MA(+) and DM(+)/MA(-) groups and 45 +/- 39.8 vs 9.9 +/- 16.6 (P < .001) in the DM(-)/MA(+) and DM(-)/MA(-) groups. Spearman correlation analysis demonstrated a positive relation between urine albumin/creatinine ratio (ACR) and extent of CAD both in the diabetic and nondiabetic patients (r = .584, P = .001; r = .545, P = .001). Microalbuminuria was found to be an independent predictor for the presence (OR for MA: 3.728; 95% CI, 1.931-7.196; P < .001) and severity of CAD ( P < .001, beta = .563). Conclusion: A strong relationship between MA and the severity of CAD was reported.