Platelet distribution width (PDW) measures the variability in platelet size and is a marker of platelet activation. We investigated whether PDW is associated with the extent of coronary artery disease (CAD) and coronary total occlusions (CTOs). We studied 162 patients: 108 had a coronary lesion with a diameter stenosis of 50%, the CAD(+) group, and 54 patients had normal coronary anatomy, the CAD(-) group. The CAD(+) group was subdivided into CAD(+) CTO(+) and CAD(+) CTO(-) groups. Among patients with CAD, the CTO(+) group had a significantly greater PDW (%) than the CTO(-) group (16.9 +/- 2.8, 15.4 +/- 3.0, and 15.4 +/- 1.9, respectively; P = .008). In a receiver-operating characteristic analysis, a PDW cut point of 15.7% was identified in patients with CTO(+) (area under curve = 0.64, 95% confidence interval 0.54-0.75). A PDW value of more than 15.7% demonstrated a sensitivity of 64% and a specificity of 66%. The PDW is a simple platelet index that may predict the presence of CTO.