['Even though anaemia has been shown to be a risk factor for adverse cardiovascular disease, there is scarce evidence of its relationship with angiographically proven coronary artery disease (CAD). The aim of this study was to evaluate the relationship between haemoglobin (Hb) levels and the extent of CAD.', 'We measured Hb, mean corpuscular volume and red blood cell count in 2363 consecutive patients undergoing coronary angiography. Patients were divided into four groups according to quartile values of Hb (≤12.2 g/dl, group 1; 12.3-13.5 g/dl, group 2; 13.6-14.6 g/dl, group 3; >14.6 g/dl, group 4).', 'Patients with lower Hb were older (P<0.001), there was a predominance of women (P<0.0001), and patients had diabetes (P<0.0001), hypertension (P=0.024), renal failure (P<0.0001), previous coronary artery bypass graft (P<0.0001), previous cerebrovascular accident (P=0.039) and platelet count (P<0.0001). In terms of angiographic features, low Hb levels were associated with a larger prevalence of calcified lesions (P<0.001), but a lower prevalence of thrombus-containing lesions (P<0.001). Hb was not associated with the prevalence of CAD [odds ratio (OR) (95% confidence interval (CI))=0.96 (0.89-1.04), P=0.35], whereas an association was observed with the severity of CAD [OR (95% CI)=0.92 (0.85-0.99), P=0.032] that was not confirmed after correction for baseline confounding factors [OR (95% CI)=0.98 (0.89-1.09), P=0.76]. Similar findings were observed for mean corpuscular volume and red blood cell count.'] Do haemoglobin levels correlate with the extent of coronary artery disease : results from a large cohort study?