Diabetic ketoacidosis (DKA) and hyperosmolar hyperglycemic state (HHS) are severe acute metabolic complications of diabetes. DKA is characterized by uncontrolled hyperglycemia, metabolic acidosis, and increased total body ketone concentration, while HHS is marked by severe hyperglycemia, hyperosmolality, and dehydration without significant ketoacidosis. These conditions result from absolute or relative insulin deficiency and increased counterregulatory hormones. DKA is more common in type 1 diabetes, but type 2 diabetes patients are also at risk during catabolic stress. The mortality rate for DKA is <1%, but it is >5% in the elderly and those with comorbidities. HHS has a higher mortality rate of 5–20%. Recent studies show an increasing trend in hospitalizations for DKA in the U.S., with a 35% increase from 1996 to 2006. Infection, discontinuation of insulin, and underlying medical illnesses are common precipitating factors. Treatment involves fluid resuscitation, correction of dehydration and hyperglycemia, and electrolyte imbalances, with frequent patient monitoring. Protocols for management include fluid therapy, insulin therapy, and potassium and bicarbonate administration. Prevention focuses on better access to care, patient education, and early recognition of signs and symptoms.Diabetic ketoacidosis (DKA) and hyperosmolar hyperglycemic state (HHS) are severe acute metabolic complications of diabetes. DKA is characterized by uncontrolled hyperglycemia, metabolic acidosis, and increased total body ketone concentration, while HHS is marked by severe hyperglycemia, hyperosmolality, and dehydration without significant ketoacidosis. These conditions result from absolute or relative insulin deficiency and increased counterregulatory hormones. DKA is more common in type 1 diabetes, but type 2 diabetes patients are also at risk during catabolic stress. The mortality rate for DKA is <1%, but it is >5% in the elderly and those with comorbidities. HHS has a higher mortality rate of 5–20%. Recent studies show an increasing trend in hospitalizations for DKA in the U.S., with a 35% increase from 1996 to 2006. Infection, discontinuation of insulin, and underlying medical illnesses are common precipitating factors. Treatment involves fluid resuscitation, correction of dehydration and hyperglycemia, and electrolyte imbalances, with frequent patient monitoring. Protocols for management include fluid therapy, insulin therapy, and potassium and bicarbonate administration. Prevention focuses on better access to care, patient education, and early recognition of signs and symptoms.