The etiopathogenesis of Behçet’s Disease is not clearly understood. Recurrent aphthous stomatitis is seen in Behçet’s Disease. Mucous membranes are protected by general host defenses, a specific immune response to damage caused by free radicals under normal conditions. Nitric oxide is a free radical that plays a role in chronic and acute inflammation and systemic inflammatory response. Our purpose was to investigate the levels of nitric oxide in serum and saliva samples from patients with Behçet’s Disease and recurrent aphthous stomatitis and from a control group. In the clinical study, 22 patients with Behçet’s Disease, 24 patients with recurrent aphthous stomatitis, and 27 healthy individuals were included. Serum and saliva samples were taken from each group to examine nitric oxide levels. When the nitric oxide levels of serum and saliva were evaluated, the only statistically significant finding was that nitrate and nitrite levels were lower in the control group than in patients with Behçet’s Disease and recurrent aphthous stomatitis. There was no difference between patients with Behçet’s Disease and patients with recurrent aphthous stomatitis. We conclude that nitric oxide levels increase in patients with Behçet’s Disease and recurrent aphthous stomatitis, both in serum and saliva. The results of nitric oxide in saliva and serum were found to be compatible. Saliva can be used to evaluate nitric oxide in Behçet’s Disease and recurrent aphthous stomatitis. Salivary nitric oxide levels may be an important marker for estimating the severity of Behçet’s Disease for clinicians.