Diabetic ketoacidosis (DKA) and nonketotic hyperglycemic hyperosmolar coma (NHHC) are the two most common acute complications of diabetes mellitus and make up a significant percentage of the nonsurgical emergencies seen in any general hospital. These syndromes have devastating outcomes if not treated promptly. The aim of this study was to evaluate clinical and biochemical characteristics of our patients with diabetic coma. In this study, patients with diabetic coma admitted to the clinics of internal medicine from 1984 to 1996 were evaluated retrospectively. Fifty eight patients (mean age 52.47 ± 17.92 years), 36 female, 22 male, were hospitalised because of diabetic coma. Seventeen patients had type I diabetes mellitus, 41 patients had type II diabetes mellitus. DKA was diagnosed in 28 patients and 30 patients had NHHC. The factors that precipitated coma were detected in 29 patients (50%), 4 patients (6.9%) had ceased insulin therapy by themselves. After the patients were admitted to the hospital, mini-insulin regimen was started in addition to fluid and electrolyte therapy. Ketonuria, blood glucose, plasma osmolality and pH, blood urea nitrogen (BUN), creatinin, sodium, potassium levels were determined before the treatment and after 24 hours of mini-insulin therapy. Ketonuria was still present in 12 patients with DKA within 24th hours of mini-insulin therapy. Hypopotassemia (27.5%) was the most common complication of the therapy. Fatality was 14.2% in patients with DKA and 36.6% in patients NHHC. There was no correlation between hypopotassemia and mortality rates. Mortality rate in patients with NHHC was higher than patients with DKA, but this difference was not statistically significant.