This study was designed to answer the following questions: (i) Do levels of serum gamma-glutamyl transferase (GGT), a marker of oxidative stress, change in hypertensive retinopathy (HR)? (ii) Is there any relation between degree of HR and GGT levels? This study included 80 hypertensive patients with HR. Group 1 comprised 40 patients with grade I HR, and group 2 comprised 40 patients with grade II HR. We selected 40 healthy subjects for the control group. Level of GGT in group 2 was significantly higher than in group 1 (P = 0.005) and control group (P = 0.001); it was also higher in group 1 than in control group (P = 0.025). Our study suggests that oxidative stress, mechanisms known to be involved in vascular lesions, may promote the development of HR.