Elevated plasma levels of inflammation and endothelial dysfunction markers have been reported in patients with hypertrophic cardiomyopathy (HCM). The aim of the current study was to determine whether HCM is associated with enhanced oxidative stress. We enrolled 54 HCM patients with sinus rhythm, including 21 subjects with a left ventricular outflow tract (LVOT) obstruction (gradient >/= 30 mmHg), and 54 age- and sex-matched controls without cardiovascular diseases. Serum levels of 8-isoprostaglandin F(2alpha) (8-iso-PGF(2alpha)), a stable marker of oxidative stress, were determined. Serum 8-iso-PGF(2alpha) levels were elevated in HCM patients compared with controls (35.4 +/- 10.2 vs. 29.9 +/- 9.9 pg/ml, p < 0.001). Patients with obstructive HCM displayed higher 8-iso-PGF(2alpha) levels compared with the non-obstructive HCM subgroup (41.6 +/- 12.7 vs. 31.4 +/- 5.4 pg/ml, p < 0.0001). Both anatomic (mitral-septal distance) and hemodynamic (subaortic gradient) indexes of LVOT obstruction, but not other echocardiographic variables, correlated with 8-iso-PGF(2alpha) levels (r = -0.43; p < 0.05 and r = 0.39; p < 0.05, respectively). This study is the first to show that HCM is characterized by enhanced oxidative stress as evidenced by higher 8-iso-PGF(2alpha), which achieves its highest values in the presence of LVOT obstruction in HCM patients.