Erectile dysfunction is a persistent inability to achieve and maintain an erection adequate for satisfactory sexual activity. Nitric oxide is the principal neurotransmitter mediating penile erection and synthesized by the enzyme nitric oxide synthase by converting oxygen and L-arginine to NO and citrulline in the cavernous nerve terminals and in the endothelium. Erectile dysfunction is associated with several disorders such as cardiovascular disease, hypertension, diabetes, obesity, testosterone deficiency and depression. It can be diagnosed on the basis of medical history. Physical examinations describe hypogonadism and vascular disease. A laboratory test includes complete blood cell count, fasting serum glucose, a lipid profile and total testosterone. The primary aim of management is to identify modifiable factor by PDE5 inhibitors, vacuum devices for inducing erection, intracavernous injection therapy and intraurethral alprostadil. Surgical treatments for erectile dysfunction described are penile prosthesis, penile revascularisation, androgen replacement therapy, melanocortin receptor agonists and gene therapy.