Nitric oxide (NO) is a short-life molecule produced by the enzyme known as the nitric oxide synthase (NOS), in a reaction that converts arginine and oxygen into citrulline and NO. There are three isoforms of the enzyme: neuronal NOS (nNOS, also called NOS1), inducible NOS (iNOS or NOS2), and endothelial NOS (eNOS or NOS3). It is now known that each of these isoforms may be expressed in a variety of tissues and cell types. This paper is a review of the current knowledge of various functions of NO in diseases. We discuss in more detail its role in Cancer, the role of NO in myocardial pathophysiology, in central nervous system (CNS) pathologies. Other diseases such as inflammation, asthma, in chronic liver diseases, inflammatory bowel disease (IBD), arthritis, are also discussed. This review also covers the role of NO in cardiovascular, central nervous, pancreas, lung, gut, kidney, myoskeletal and chronic liver diseases (CLD). The ubiquitous role that the simple gas nitric oxide plays in the body, from maintaining vascular homeostasis and fighting infections to acting as a neurotransmitter and its role in cancer, has spurred a lot of interest among researchers all over the world. Nitric oxide plays an important role in the physiologic modulation of coronary artery tone and myocardial function. Nitric oxide from iNOS appears to be a key mediator of such glial-induced neuronal death. The high sensitivity of neurons to NO is partly due to NO causing inhibition of respiration, rapid glutamate release from both astrocytes and neurons, and subsequent excitotoxic death of the neurons.