Objectives: The purpose of this research was to study the association between nonsignificant(< 50%) left main coronary artery disease(LMCAD) and short-and long-term survival in patients undergoing percutaneous coronary intervention(PCI). Background: The prognostic importance of nonsignificant LMCAD is unknown; however, the co-existence of nonsignificant LMCAD may influence revascularization decisions. Methods: We analyzed mortality and repeat catheterization rates of 11,855 patients in a prospective cardiac registry database who underwent single-vessel or multivessel PCI from January 1996 through December 2001. Of this cohort, 11.7%(n= 1,385) had nonsignificant(< 50%) LMCAD. Outcomes were compared with those without LMCAD. A secondary analysis was performed on a larger cohort of 34,586 patients undergoing cardiac catheterization, irrespective of mode of revascularization therapy. Results: Patients with nonsignificant LMCAD had more co-morbidities, and a significantly higher crude mortality rate at 1 year compared with those without LMCAD(4.4%vs. 3.4%; p=0.05). The 7-year crude mortality hazard ratio(HR) of PCI patients with< 50%LMCAD versus those with no LMCAD was 1.18(95%confidence interval[CI] 0.94 to 1.46). After risk adjustment for differences in baseline clinical profile, however, the HR decreased to 0.98(95%CI 0.79 to 1.23). Repeat catheterization rates at 1 year did not differ between groups. The secondary analysis in all patients with nonsignificant LMCAD showed an adjusted HR of 1.03(95%CI 0.94 to 1.14). Conclusions: Patients undergoing single-vessel or multivessel PCI who have< 50%LMCAD have a nonsignificantly increased 18%relative risk for mortality compared with those without detectable LMCAD that appears to be related to these patients’higher incidence of co-morbidities rather than the left main stenosis itself. Objectives: The purpose of this research was to study the association between nonsignificant (<50%) left main coronary artery disease (LMCAD) and short-and long-term survival in patients undergoing percutaneous coronary intervention (PCI). Background: The prognostic importance of nonsignificant LMCAD is unknown; however, the co-existence of nonsignificant LMCAD may influence revascularization decisions. Methods: We analyzed mortality and repeat catheterization rates of 11,855 patients in a prospective cardiac registry database who underwent single-vessel or multivessel PCI from January 1996 through Of this cohort, 11.7% (n = 1,385) had nonsignificant (<50%) LMCAD. Outcomes were compared with those without LMCAD. A secondary analysis was performed on a larger cohort of 34,586 patients undergoing cardiac catheterization, irrespective of mode of revascularization therapy. Results: Patients with nonsignificant LMCAD had more co-morbidities, and a significantly higher crude morta lity rate at 1 year compared with those without LMCAD was 4.4% vs 3.4%; p = 0.05. The 7-year crude mortality hazard ratio (HR) of PCI patients with <50% LMCAD versus those with no LMCAD was 1.18 ( 95% CI 0.94 to 1.46). After risk adjustment for differences in baseline clinical profile, however, the HR decreased to 0.98 (95% CI 0.79 to 1.23). Repeat catheterization rates at 1 year did not differ between groups. The secondary analysis in all patients with nonsignificant LMCAD showed an adjusted HR of 1.03 (95% CI 0.94 to 1.14). Conclusions: Patients undergoing single-vessel or multivessel PCI who have <50% LMCAD have a nonsignificantly increased 18% relative risk for mortality compared with those without detectable LMCAD that appears to be related to these patients’higher incidence of co-morbidities rather than the left main stenosis itself.