Stress hyperglycemia is the elevation of serum glucose found in a patient, once he is admitted in the hospital. The objective of this study was to evaluate the impact of admission serum glucose level in the outcome of noncritical hospitalized patients. A prospective analytical cohort study was conducted in patients hospitalized in the Internal Medicine service of the Hospital de Especialidades, Centro Médico Nacional Siglo XXI (Instituto Mexicano del Seguro Social), from September 2011 to February 2012. We included 89 patients with serum glucose level < 110 mg/dL (group A) and 90 patients with serum glucose > 110 mg/dL (group B). Diabetes mellitus was more frequent in group B (p < 0.001). Glycosylated hemoglobin greater than 6.5 % was found in 36.4 % of the patients in group B and in 8.7 % in group A (p < 0.001). Patients in group B had higher APACHE II score (p = 0.02) and worse in-hospital outcomes. Stress hyperglycemia was associated with higher APACHE II score and more medical complications, such as sepsis, urinary tract infection, pneumonia and use of pressor amines. Mortality independent predictors were systemic arterial hypertension and APACHE II score.