Anticholinesterase insecticides are the most widely used insecticides worldwide that may cause serious poisoning. Toxicity is produced by acetylcholine accumulation at cholinergic receptors. The mortality rate for poisoned patients remains high and this makes further research on factors that may affect the final outcome necessary. The main causes of death due to acute anticholinesterase insecticides poisoning include acute respiratory failure and the cardiovascular complications. This retrospective study was conducted to assess the patterns of presentations of acute severe anticholinesterase insecticide poisoning in both children and adults, and to demonstrate the clinical and investigative determinants to intensive care unit (ICU) admission in both groups of patients. Moreover, to study the outcomes and predictors of mortality in these patients who require intensive care therapy. This study included a total of 117 patients with severe anticholinesterase insecticide poisoning, of whom 78 were adults and 39 were children. They were admitted to the ICU of the Poison Control Center of Ain Shams University Hospitals (PCC) during the period from the 1st of January 2006 to the 1st of January 2007. Data obtained were divided into quantitative variables, and qualitative variables. Data was statistically analyzed using a PC supplied with the “Statistical Package for Social Sciences” (SPSS) – version 0.8. The clinical determinants for ICU admission in adults were mainly tachycardia and hypertension, while, in children were mainly absence of nausea and vomiting, muscle weakness, agitation, confusion, fasciculations, and pulmonary edema. Regarding the investigative determinants for ICU admission in adults in the present study, these were hypokalemia, decreased pO2, increased pCO2, decreased pH. As for children, the significant decrease in k+ level, the marked decrease in O2 saturation, pO2, and pH, and the high level of pCO2 with marked acidosis.