Diabetic ketoacidosis and hyperglycaemic hyperosmolar syndrome are two acute complications of diabetes that may result in high mortality. Effective standardized treatment protocols, as well as prompt identification and treatment of the precipitating cause, are important factors affecting outcome. The authors review the pathomechanism, clinical features, complications and current recommendations for management of ketoacidosis and hyperglycaemic hyperosmolar syndrome. In patients with type 2 diabetes may develop anaerobic (type A) lactic acidosis from tissue hypoxia, while aerobic (type B) lactic acidosis is a rare complication of biguanide therapy if contraindications to metformin are observed. Mortality remains very high, especially when serious comorbidities are present. Hypoglycaemia is a major factor preventing patients with both type 1 and type 2 diabetes from achieving near-normal plasma glucose targets. The authors summarize clinical presentation and therapeutic possibilities of hypoglycaemia on the basis of the literature.