AimsInvestigate the importance of treating diabetes by evaluating mortality risk of untreated and medically-treated diabetic patients. MethodsHistorical prospectively collected observational data of hospitalized patient ≥18years, admitted for any-cause to medical wards, between January 2011 and December 2013. Main outcome was all-cause mortality at end of follow-up. ResultsCohort included 35,340 patients (51% male, median age 70years); 24,159 without diabetes and 11,181 with diabetes. Within the diabetic group, 2,188 patients (20%) were not receiving medical treatment for diabetes and 8993 were being treated as follows: 4550 (41%) non-insulin monotherapy; 1550 (14%) non-insulin combination therapy; 2,893 (26%) insulin. Hazard ratios were compared for the entire follow-up, indicating a significant difference in overall survival between medically untreated DM and all groups, except insulin-treated. Subset analysis with adjustment for age, gender, BMI, alcohol and smoking indicated a significant survival difference between untreated DM and all groups. Rates of hypertension, ischemic heart disease, renal failure, and congestive heart disease were higher in the untreated and insulin-treated diabetic patients than in the nondiabetic and diabetic patients on non-insulin treatment. ConclusionsLack of treatment for diabetes might have serious consequences. Further studies are needed to see if targeted treatment approach may decrease mortality.