Nitric oxide(NO) is not only important in host defense and homeostasis but it is also regarded as harmful and has been implicated in the pathogenesis of a wide variety of inflammatory and autoimmune diseases. The presence of NO in periodontal disease may reflect the participation of an additional mediator of bone resorption responsible for disease progression. The aim of this study was to assess the level of NO in serum and GCF in chronic periodontitis, and correlate these levels with the severity of periodontal disease. Ninety subjects participated in the study and were divided into three equal groups. NO levels were assayed by measuring the accumulation of stable oxidative metabolite, nitrite with Griess reaction. Results showed subjects with periodontitis had significantly high nitrite in serum and GCF than healthy subjects. NO levels increased with severity of periodontal disease. With the understanding of pathophysiology of NO in periodontitis selective inhibition of NO may be of therapeutic utility in limiting the progression of periodontitis.