Although an association between elevated leucocyte count and mortality in patients with ACS (acute coronary syndromes) has been established, the independence of this association from coronary risk factors and C-reactive protein has been inadequately studied. In the present study, this prospective registry included 4329 patients with ACS treated with PCI (percutaneous coronary intervention): 1059 patients with STEMI [ST-segment elevation MI (myocardial infarction)], 1753 patients with NSTEMI (non-STEMI) and 1517 patients with unstable angina. Blood samples were obtained before angiography for leucocyte count and C-reactive protein measurements. The primary outcome of this analysis was 1-year mortality. At 1 year, 345 patients (8%) had died: 45 patients in the 1st tertile, 93 patients in the 2nd tertile and 207 patients in the 3rd tertile of leucocyte count [Kaplan-Meier estimates of mortality, 3.2%, 6.4% and 14.1% with an OR (odds ratio)=2.42, 95% CI (confidence interval)1.78-3.12; P<0.001 for tertile 3 compared with tertile 2 and an OR=1.99, 95% CI 1.77-2.25; P<0.001 for tertile 2 compared with tertile 1]. The Cox proportional hazards model adjusting for coronary risk factors, ACS presentation, extent of coronary artery disease, C-reactive protein and other covariates identified leucocyte count with a HR (hazard ratio)=1.05 (95% CI 1.02-1.07; P<0.001 for 1000 cells/mm(3) increase in the leucocyte count), but not C-reactive protein (HR=1.13, 95% CI 0.95-1.34; P=0.15 for a 1 tertile increase in the C-reactive protein concentration) as an independent correlate of 1-year mortality. We conclude that elevated leucocyte count, but not C-reactive protein, predicts 1-year mortality independent of cardiovascular risk factors across the entire spectrum of patients with ACS treated with PCI.