A 33-year-old woman was admitted to our emergency department in a state of unconsciousness after attempting suicide with unknown substances. Severe metabolic acidosis (pH: 6.81), with a high anion gap (36.2) and high lactate level (20.2 mmol/L), was observed. After four hours of intensive medical treatment, the patient regained consciousness, with a return of the arterial pH to 7.42. Finally, cyanide intoxication was diagnosed based on the detection of a serum cyanide level of 3.5 mg/L. The presence of a high anion gap associated with severe lactic acidosis is a clue for making a rapid differential diagnosis of acute cyanide intoxication. Providing intensive and immediate supportive management is also crucial, even in cases without obtainable specific antidotes.