With increasing incidence of diabetes mellitus, complications associated with it are also increasing. The hyperglycemic hyperosmolar state (HHS) is one of the common complications seen in old diabetics where patients have markedly increased serum glucose concentrations and hyperosmolality in absence of significant ketosis. Most common precipitating factor is infection. In HHS, levels of insulin in circulation reduce significantly while counterregulatory or stress hormones such as cortisol, catecholamines, glucagon, and growth hormone increase along with greater degree of dehydration. Hence, these patients, in addition to typical features of diabetes, generally present with dehydration and progressive mental deterioration. Basic hematological, biochemical, and radiological investigations are important to find and rule out precipitating factors and complications. Aggressive correction of the fluid and electrolyte imbalance along with the maintaining levels of insulin are very important components of the treatment. Simultaneously, identification and treatment of any underlying precipitating events should be done. Awareness, early diagnosis, and aggressive proper treatment play very crucial role in preventing the morbidity and mortality associated with HHS, which is 10 times more than diabetic ketoacidosis.