OBJECTIVE To determine the outcome in patients with acute overdose requiring admission to the Intensive Care Unit (ICU). METHODS Prospective survey of all overdose admissions to an ICU over a six-year period ending January 1991. METHODS Tertiary referral adult teaching hospital. METHODS 732 consecutive patients with acute overdose. METHODS Death rate, use and duration of mechanical ventilation, type of compound taken and compounds associated with a fatal outcome. RESULTS The 732 patients represented 13.8% of all admissions and 6% of the available ICU bed-days. Comparison with all admissions to the Emergency Department for acute overdose over a 27-month period ending April 1990 indicated that 22% of these patients were admitted to the ICU. Among the patients admitted to the ICU, tricyclic antidepressants, benzodiazepines and alcohol were the most frequently used compounds. More than one compound had been taken by 46.8% of the patients. Mechanical ventilation was required in 79.5% of the patients and 14 (2%) died. CONCLUSIONS Acute overdose is a common cause of admission to the ICU but has a mortality rate of only 2%. In contrast to the overdoses taken by survivors, patients taking fatal overdoses are more likely to have taken a large dose of a single drug, or a non-medicinal compound.