Introduction. Clinical scoring systems are used to predict mortality rate in hospitalized patients. Their utility in organophosphate (OP) poisoning has not been well studied. Methods. In this retrospective study of 396 patients, we evaluated the performance of the Acute Physiology and Chronic Health Evaluation (APACHE) II score, the Simplified Acute Physiology Score (SAPS) II, Mortality Prediction Model (MPM) II, and the Poisoning Severity Score (PSS). Demographic, laboratory, and survival data were recorded. Receiver operating characteristic (ROC) curves were generated, and the area under the curve (AUC) was calculated to study the relationship between individual scores and mortality rate. Results. The mean (standard deviation) age of the patients was 31.4 (12.7) years, and at admission, their pseudocholinesterase (median, interquartile) level was 317 (222-635) U/L. Mechanical ventilation was required in 65.7% of the patients and the overall mortality rate was 13.1%. The mean (95% confidence interval) scores were as follows: APACHE-II score, 16.4 (15.5-17.3); SAPS-II, 34.4 (32.5-36.2); MPM-II score, 28.6 (25.7-31.5); and PSS, 2.4 (2.3-2.5). Overall, the AUC for mortality was significantly higher for APACHE-II (0.77) and SAPS-II (0.77) than the PSS (0.67). When patients were categorized, the AUCs were better for WHO Class II (0.71-0.82) than that for Class I compounds (0.60-0.66). For individual compounds, the AUC for APACHE-II was highest in quinalphos (0.93, n = 46) and chlorpyrifos (0.86, n = 38) and lowest in monocrotophos (0.60, n = 63). AUCs for SAPS-II and MPM-II were marginally but not significantly lower than those for APACHE-II. The PSS was generally a poorer discriminator compared to the other scoring systems across all categories. Conclusions. In acute OP poisoning, the generic scoring systems APACHE-II and SAPS-II outperform the PSS. These tools may be used to predict the mortality rate in OP poisoning.