BACKGROUND: Survival after acute myocardial infarction (MI) is linked to multiple factors, including mild or severe chronic kidney dysfunction. The aim of this study was to determine to what extent a reduction in glomerular filtration rate (GFR) influences 1-year mortality when risk level at admission and quality of care are taken into account. METHODS: A prospective registry was carried out in a geographically delimited area, including all patients admitted with a diagnosis of acute MI over a 6-month period. The GFR was calculated from serum creatinine levels, and patients were stratified into 3 groups: GFR1 >59 mL/min per 1.73 m2, GFR2 >29 and <60 mL/min per 1.73 m2, and GFR3 <30 mL/min per 1.73 m2. A risk index based on initial presentation was calculated. Inhospital and discharge treatments were recorded, taking into account possible contraindications. Patients were followed up for 1 year to assess all-cause mortality rate. RESULTS: A total of 754 patients were included, 333 ST-elevation MI and 421 non-ST-elevation MI. Overall 1-year mortality was 11.5%. Patients with impaired GFR were older, with more comorbidities, and received fewer effective therapies (less reperfusion, glycoprotein IIb/IIIa receptor inhibitors, early angiography, beta-blockers, and statins). One-year mortality increased as GFR decreased: GFR1 2.3% (5/215), GFR2 9.4% (31/328), and GFR3 24.2% (51/211) (P < .001 for trend). By multivariable logistic regression, a significant association was found between 1-year mortality and risk index (odds ratio [OR] 1.41, 95% CI 1.16-1.71 per 10% increase in risk index), GFR (OR 0.97, 95% CI 0.95-0.98 per additional GFR unit), use of beta-blockers (OR 0.15, 95% CI 0.05-0.50 for users), and early coronary angiography (OR 0.26, 95% CI 0.32-0.66 for patients submitted to angiography). CONCLUSIONS: In patients with acute MI, decreased GFR is associated with higher mortality, and this relation remains strong after adjustment for the level of risk at admission and the effective treatments used.