Objective . The aim of this study was to evaluate the Acute Physiology and Chronic Health Evaluation (APACHE) II, III and Simplified Acute Physiology Score II (SAPS II) as predictors of severity of organophosphate poisoning (OPP). Methods . This is a retrospective study of 48 patients with OPP who were admitted to the intensive care unit (ICU) for at least 24 h between 1997 and 2004. Demographic, laboratory, survival data and on day one APACHE II, III, SAPS II and Glasgow Coma Scale (GCS) were recorded, and correlations between these scores and severity of poisoning were performed. Results . Forty-eight patients were evaluated. Mechanical ventilation was required by 58% of patients. The mean APACHE II, III and SAPS II values were 11.5 +/- 7.21, 42.1 +/- 24.49 and 25.1 +/- 15.76, respectively. Total dose and duration of atropine and of pralidoxime therapy, length of ICU stay and mortality all correlated with these clinical scoring tools. Conclusions . The APACHE II, III and SAPS II clinical scoring tools seem to predict the severity of organophosphate poisoning, and may have prognostic value.