Nitric oxide synthase gene is present on chromosome 17 and has been implicated in a wide variety of diseases. The nitric oxide synthase enzyme forms nitric oxide that besides being a signalling molecule plays an important role in host immune response. Inducible nitric oxide synthase expression is regulated at the level of transcription. Single-nucleotide polymorphisms, copy number variation and simple sequence repeat are important variations that have been reported in human genome. The presence of such variations in the regulatory region affects the level of gene product in the cell, while variation in the coding region influences the structure of proteins and its activity. This alteration in the level of gene product and the structure of the protein molecule might be responsible for the final outcome of genetic as well as infectious diseases. In the present manuscript, we review the role of inducible nitric oxide synthase (iNOS) gene polymorphisms in different diseases and populations. The iNOS gene with one pentanucleotide repeat, two single-nucleotide polymorphisms in promoter region and one polymorphism in exon 16 has been implicated in several diseases. We have also predicted several polymorphisms in the promoter region of iNOS computationally, which might affect the transcription factor binding site (TFBS) and hypothesize that these polymorphisms have some putative role in the outcome of disease(s).