Background: Growth hormone deficiency (GHD) is associated with an increased cardiovascular mortality. Increased oxidative stress has been associated with development of cardiovascular and cerebrovascular diseases. In the present study, we aimed to evaluate oxidant and antioxidant status in patients with GHD by analyzing serum paraoxonase1 (PON1) activity, and malondialdehyde (MDA) and thiol levels. Materials and Methods: This study was a case-control study. Thirty patients with GHD were included in the study and compared with 20 healthy controls. Serum PON1 activity, and MDA and thiol levels were measured according to an enzymatic spectrophotometric method. Results: Serum MDA levels (2.8 +/- 1.3 nmol/mL) were higher in GHD group than the controls (1.7 +/- 0.5 nmol/mL) (P = 0.001). PON1 activity (149.9 +/- 77.9 U/L) was lower in GHD group than the controls (286.3 +/- 126.7 U/L) (P = 0.001). Thiol and high-density lipoprotein cholesterol (HDL-cholesterol) levels were lower in GHD group (218.6 +/- 103.9 mu mol/L and 32.6 +/- 13.4 mg/dL, respectively) than the controls (289.6 +/- 101.1 mu mol/L and 54.3 +/- 14.9 mg/dL, respectively) (P = 0.021 and P = 0.001, respectively). In GHD patients, serum MDA level was negatively correlated with serum HDL-cholesterol (r = -0.499, P = 0.001), and serum PON1 activity was positively correlated with serum thiol and HDL-cholesterol levels (r = 0.306, P = 0.032 and r = 0.303, P = 0.033, respectively). Conclusion: These data support that GHD is characterized by an imbalance between oxidant and antioxidant factors. This abnormality may contribute to the increased atherogenic risk in patients with GHD.