Inpatient hyperglycemia in people with or without diabetes is associated with an increased risk of complications and mortality, a longer hospital stay, a higher admission rate to the intensive care unit, and higher hospitalization costs. Despite increasing evidence that supports intensive glycemic control in hospitalized patients, blood glucose control continues to be challenging, and sliding scale insulin coverage, a practice associated with limited therapeutic success, continues to be the most frequent insulin regimen in hospitalized patients. Sliding scale insulin has been in use for more than 80 years without much evidence to support its use as the standard of care. Several studies have revealed evidence of poor glycemic control and deleterious effects in sliding scale insulin use. To understand its wide use and acceptance, we reviewed the origin, advantages, and disadvantages of sliding scale insulin in the inpatient setting.