Aim of the study: The aim was to investigate whether serum vitamin D concentration is decreased due to the increased nitrite concentration in female patients suffering from glaucoma and ocular hypertension. Correlation of clinical parameters with serum vitamin D level was compared to determine vitamin D association with glaucomatous optic neuropathy. Vitamin D hypovitaminosis leads to lower nitric oxide synthase (NOS) inhibition, i.e. to increased NOS, greater nitric oxide production and higher peroxynitrite toxicity. Nitric oxide induces release of glutamate and neuronal toxicity, which is one of the causes of glaucomatous optic neuropathy development. Our hypothesis was based on this pathophysiological association. The presence of vitamin D receptors has been demonstrated in many structures of the human eye. Thus, vitamin D immunomodulatory action may be postulated in the presence of a sufficient vitamin D concentration. Study design: Observational cross-sectional study with control group. Subjects and methods: The study included 90 women aged 45-55 suffering from glaucoma (patient group) and 50 age-matched women free from glaucoma (control group). All study subjects underwent ophthalmologic examination and determination of vitamin D and nitrite serum concentrations. Results: The left eye intraocular pressure was significantly higher in glaucoma patients as compared with control subjects (t-test=-2.617; p=0.01). The mean c/d ratio showed a statistically significant between-group difference (t-test=9.257; p<0.001). There was a statistically significant between-group difference in MD index on both left and right eyes (t- test=2.693; p=0.008 and t-test=3.006; p=0.003, respectively). The mean serum vitamin D concentration was 40.6 nmol/L in patient group and 50.43 nmol/L in control group, yielding a statistically significant difference (t-test=2.188; p=0.031). Accordingly, the mean serum vitamin D concentration was higher in the control group of women free from glaucoma. Vitamin D deficiency was recorded in a comparable proportion of subjects from both groups. Normal serum vitamin D concentration was found in 40% of control subjects versus 27.8% of glaucoma patients. Distribution of subjects according to vitamin D concentration did no differ significantly between the patient group and control group (%2-test=2.210; p=0.331). In the group of glaucoma patients, serum vitamin D concentration was not age dependent but was comparable in both age groups (40,99 vs. 40,43 nmol/L). In younger age group, the mean serum vitamin D concentration was 61.44 nmol/L, yielding a statistically significant difference (i-test=3.832; p<0.001). It should be noted that the mean serum vitamin D concentration measured in this age group exceeded the mean vitamin D concentration recorded in this group as a whole (50.43 nmol/L). The mean serum nitrate/nitrite (NO3-/NO2-) concentration was 15.48 ^mol/L and 12.93 pmol/L in the patient group and control group, respectively, yielding no statistically significant between-group difference but justifying the study hypothesis. Nitrites were not statistically significantly associated with vitamin D in either group of subjects. There was no association of serum vitamin D concentration with the disease severity (MD index) either. Conclusion: Our results suggest that serum level of vitamin D could serve as a marker associated with the presence of glaucoma but not with the disease severity. However, it remains obscure whether the association of lower serum vitamin D concentration and glaucoma is causal or not. Since, in female patients with glaucoma the increased amount of nitrites is not found, it can be concluded that NO is not involved in the protective effect of vitamin D on glaucoma. Vitamin D insufficiency is associated with neurodegenerative disorders including glaucomatous optic neuropathy.