Background: Many people are still getting affected by uncontrolled glycemic events during hospital admission, which encompasses hypoglycemia, hyperglycemia, and high glycemic variability. Introduction: Primary studies have shown an association of glycemic dysregulation with increased length of hospital stay and mortality among overall patients, however, there is no systematic review of current evidence on the association between uncontrolled in-hospital glycemia in patients with diabetes and health outcomes. This study aimed to systematically review the current evidence on the association between uncontrolled in-hospital glycemia in patients with diabetes and health outcomes. Methods: The association between glycemic dysregulation and health outcomes for inpatients with diabetes was systematically reviewed. PubMed, Embase, and LILACS databases were searched. Two independent reviewers were involved in each of the following steps: screening titles, abstracts, and fulltexts; assessing the methodological quality; and extracting data from included reviews. Descriptive analysis method was used. Results: Seven cohort studies were included, and only two had a prospective design, consisting of 7,174 hospitalized patients with diabetes. In-hospital occurrence of hypoglycemia, hyperglycemia, and glycemic variability were assessed, and outcomes were mortality, infections, renal complications, and adverse events. Among the exposure and outcomes, an association was observed between severe hypoglycemia and mortality, hyperglycemia and infection, and hyperglycemia and adverse events. Conclusion: In-hospital uncontrolled glycemia in patients with diabetes is associated with poor health outcomes. More studies should be conducted for proper investigation because diabetes is a complex condition. Effects of glycemic dysregulation should be investigated on the basis of overall health of a patient instead from only organ-target perspective, which makes the investigation difficult.