Background and objectives: HbA1c shows the mean glucose level in blood and is a biochemical parameter used in follow-up and diagnosis of diabetic patients. We aimed to investigate the association between HbA1c and in-hospital all cause mortality in diabetic patients who were admitted due to any diagnosis. Methods: 3207 diabetic patients included study who had been diagnosed with diabetes mellitus. Trauma patients, type 1 diabetes were excluded. Patients’ age, gender, admission diagnosis, duration of hospitalization, whether they died in-hospital, laboratory parameters and HbA1c levels were recorded. Results: The mean age of patients was 50.53±17 years with 59.7 % (n:1913) being females. Patients who died in hospital had higher HbA1c, age, BUN (blood urea nitrogen), creatine and uric acid levels according to the Univariate analysis (p = 0.000, p = 0.000; p = 0.004, p = 0.04, p = 0.03; respectively). In the model 1 in multivariate analysis, there was a significant correlation between HbA1c level and in-hospital mortality (uncorrected OR: 1.216, 95 % CI 1.116-1.326,p < 0.001). In the model 2, the significant correlation between HbA1c level and in hospital mortality continued when corrected with age and gender (corrected OR: 1.150, 95 % CI 1.046-1.265, p : 0.004). In the model 3, which was created with covariates that were found significant in the univariate analysis, the correlation between HbA1c level and in hospital mortality still continued (corrected OR: 1.151, 95 % CI 1.041-1.271, p : 0.006). Interpretation and conclusions: There was a positive correlation between in hospital all cause mortality and HbA1c level in diabetic patients who had admitted any diagnosis. HbA1c level predict in hospital short term all cause mortality.