We used virtual histology and intravascular ultrasound (VH-IVUS) to evaluate the relation between aortic knob calcium (AKC) and plaque components in diabetic patients. The presence of AKC was assessed by posteroanterior view of chest x-ray or fluoroscopy at the time of coronary angiography. A total of 137 de novo coronary culprit lesions in 137 consecutive diabetic patients were studied and coronary plaque components were analyzed using VH-IVUS according to the presence (n = 45) or absence (n = 92) of AKC. Patients with AKC were significantly older (68 ± 8 vs 62 ± 9 years, p <0.001) and had significantly higher high-sensitivity C-reactive protein levels (1.97 ± 1.33 vs 0.48 ± 1.35 mg/dl, p = 0.005) compared to patients without AKC. Absolute and percent necrotic core (NC) volumes (30 ± 26 vs 20 ± 19 mm³, p = 0.003; 23.4 ± 10.3% vs 17.4 ± 8.9%, p = 0.005, respectively) and absolute and percent dense calcium (DC) volumes (17 ± 12 vs 11 ± 12 mm³, p = 0.010; 13.3 ± 7.3% vs 9.6 ± 7.9%, p = 0.011, respectively) were significantly greater in lesions with AKC compared to those without AKC. Multivariable analysis showed that age (odds ratio [OR] 1.233, 95% confidence interval [CI] 1.121 to 1.355, p <0.001), high-sensitivity C-reactive protein (OR 1.871, 95% CI 1.090 to 2.943, p = 0.007), absolute DC volume (OR 1.020, 95% CI 1.050 to 1.178, p = 0.003), and absolute NC volume (OR 1.026, 95% CI 1.057 to 1.199, p <0.001) were independent predictors of AKC. In conclusion, diabetic patients with AKC were older, had greater NC- and DC-containing plaques, and higher inflammatory status compared to diabetic patients without AKC.