There has been much debate concerning an invasive versus a conservative strategy for patients with acute coronary syndromes. The purpose of this study was to determine whether early in-hospital catheterization reduced mortality in patients with unstable angina and non-ST-elevation myocardial infarction. We performed a retrospective analysis of data collected in the Global Use of Strategies to Open Occluded Coronary Arteries (GUSTO) IIb trial, which compared hirudin and heparin in patients with acute coronary syndromes. We identified 8011 patients with non-ST-segment elevation myocardial infarction and unstable angina who were enrolled in the trial. The primary endpoints were all-cause mortality at 30 days and 1 year. Data were analyzed with multivariate hazards models and propensity scores.After accounting for inception time bias, there were 7897 patients identified, of whom 4536 patients (57%) underwent invasive therapy and 3361 (43%) underwent conservative therapy. Adjusting for propensity scores, the adjusted 30-day mortality for the invasive group was 2.5% compared with 2.7% in the conservative group (P = 0.92); at 1 year, the invasive group had a 6.2% mortality, versus 8.6% in the conservative group (P = 0.005). In a multivariate analysis that adjusted for other clinical factors, an invasive strategy was associated with lower 1-year mortality (hazard ratio = 0.46; 95% confidence interval: 0.10 to 0.84). In patients presenting with acute coronary syndromes, an invasive strategy is associated with improved survival at 1 year even after adjusting for baseline differences.