Hypoglycemia is a major limiting factor in the glycemic control of patients with diabetes . Mild episodes markedly impact quality of life. Severe events are associated with adverse clinical outcomes and represent a remarkable burden to the healthcare systems [2–4]. Considering the impact of hypoglycemia on overall patients’ survival and on healthcare services, strategies to reduce the hypoglycemic risk are needed in diabetes management programs . Health authorities often rely on administrative data to assess the magnitude of public health problems in order to set up interventions able to improve disease management and patient care. Nonetheless, accuracy and validity of such data, including International Classification of Diseases, 9th revision, Clinical Modification (ICD-9-CM) codes, widely differs across diseases and settings. There is evidence that hypoglycemia may represent a marker of vulnerability. Several studies found degrees of association between hypoglycemia and adverse cardiovascular events . Furthermore, diabetic patients with recurrent hypoglycemia are characterized by multiple comorbidities [2, 3]. As a consequence, associated events and diseases may represent the drivers of hospital admission following correction of hypoglycemia, being subsequently reported as main diagnoses in the hospital discharge records. Hypoglycemia may thus be at risk of underreporting, and the ICD-9-CM coding for hypoglycemia could be especially susceptible to errors. Using data derived from the HYPOglycemia Treatment in the Hospital Emergency System—Italian Study (HYPOTHESIS) , we aimed to determine whether the ICD-9-CM codes for hypoglycemia were correctly reported in the hospital discharge records of diabetes patients hospitalized following a referral to the emergency department (ED) for a hypoglycemic event.