Background: We evaluated the gender differences in plaque components in acute coronary syndrome (ACS) patients. Methods: We used virtual histology-intravascular ultrasound (VH-IVUS) to evaluate the plaque components in culprit lesions in 362 ACS patients (254 men, 108 women). Thin-cap fibroatheroma (TCFA) was defined as focal, necrotic core (NC)-rich (��� 10% of the cross-sectional area) plaques being in contact with the lumen in a plaque burden ��� 40%. Results: Women were more diabetics (34% vs. 23%, P = 0.030), had greater %NC volume (19.0짹12.7% vs. 16.8짹11.9%, P = 0.040), and had trends toward higher high-sensitivity C-reactive protein (hs-CRP) (0.85짹1.28 vs. 0.53짹0.48 mg/dl, P = 0.063) and higher incidence of TCFA (62% vs. 52%, P = 0.078) compared with men. %NC volume was significantly greater in diabetic patients compared with nondiabetic patients (20.4짹10.2% vs. 16.0짹8.9%, P < 0.001). When we compared the plaque components between diabetic women and men, there were no differences between both groups. %NC volume was significantly greater in patients with elevated hs-CRP (���0.3mg/dl) compared with those with normal hs-CRP (<0.3mg/dl) (19.1짹8.9% vs. 16.1짹9.7%, P = 0.002). When we compared the plaque components between women and men with elevated hs-CRP levels, there were no differences between both groups. Diabetes (OR: 2.44, 95% CI: 1.35-3.82, p=0.003) and hs-CRP (OR; 1.54, 95% CI=1.08-2.65, p=0.032), but not female gender, were the independent predictors of TCFA. Conclusion: Although women ACS patients have more vulnerable plaque components (NC-rich plaque) compared with men ACS patients, these findings may be resulted from not true gender differences in plaque components but higher prevalence of diabetes and hs-CRP elevation in women.