Hyperglycemia occurring during hospitalization is a common phenomenon among patients with or without a known history of diabetes mellitus. For several years, hyperglycemia in hospitalized patients had been considered as an accompanying characteristic of the acute disease that resulted in admission. That point of view changed over time mainly because of emerging indications from clinical studies showing that hyperglycemia during hospitalization could aggravate prognosis and increase mortality. Further studies engaged on how hyperglycemia should be treated, yielded results that highlighted the increasing risk of mortality due to hypoglycemia in such efforts and also questioned the initial relation between hyperglycemia during hospitalization and a poor prognosis. Based on the fact that there is still no common ground on what is the best approach on hyperglycemia of hospitalized patients, the best practice remains to follow a different regime with different glycemic goals for different patient groups. In this review, hospitalized patients are divided into three groups; intensive care unit patients (general and cardiac), non-intensive care unit patients (general and cardiac) and peri-operative patients.