The aim of this study was to determine by multivariate analysis how alcohol and other factors affect the clinical course and outcome in patients with acetaminophen (paracetamol) poisoning. A total of 645 consecutive patients admitted from 1994 to 2000 with single-dose acetaminophen poisoning were studied, giving special attention to alcohol history, time between overdose and intravenous N-acetylcysteine (NAC) treatment ("time to NAC"), and other data available at the time of admittance. Up until 72 hours after ingestion, time to NAC was the single most important independent risk factor. With a time to NAC less than 12 hours, the mortality rate was 0.42% (95% CI, 0.05-2.7). When time to NAC exceeded 12, 24, and 48 hours, the mortality rate increased to 6.1%, 13%, and 19%, respectively. Chronic alcohol abuse was an independent risk factor of mortality (odds ratio [OR], 3.52; 95% CI, 1.78-6.97). Acute alcohol ingestion was an independent protective factor regarding mortality in alcoholic patients (OR, 0.08; 95% CI, 0.01-0.66) but not in nonalcoholic patients (OR, 0.21; 95% CI, 0.03-1.67). Patient age and quantity of acetaminophen were independent risk factors. In conclusion, time to NAC was confirmed as the major risk factor in acetaminophen-induced hepatotoxicity and mortality. Chronic alcohol abuse was an independent risk factor that could be counteracted by concomitant acute alcohol ingestion. We suggest that patients with chronic alcoholism and suspected acetaminophen poisoning due to an increased risk of developing hepatotoxicity should be treated with NAC regardless of risk estimation.