BACKGROUND: Acid-base and electrolytes disturbance is an important cause of deaths in intensive care unit patients, so it is necessary to have a broader analysis of their effects in the prediction of the outcome among critically ill poisoned patients. AIM: To evaluate the role of acid-base and electrolytes as predictors of the outcome in critically ill poisoned cases. METHODS: This was a prospective study conducted on 181 cases of critically poisoned patients admitted to ICU in Menoufia Poison Control Center (MPCC) from the beginning of January 2020 till the end of June 2020. A clinical toxicological sheet was fulfilled for every case including patient's sociodemographic data, clinical data of patient's assessment, poison severity scoring (PSS), investigations done for the cases as biochemical laboratory investigations; including arterial blood gases, serum electrolytes, renal and liver functions, and specific toxicological screening tests for detection of poisons. Cases were divided according to their outcome into survivors and non-survivors. All data were collected and statistically analyzed. RESULTS: 181 cases of critically ill poisoned patients were included in the study. Males represented (51.4%), while females were (48.6%). Cases from rural areas outnumbered those from urban, ingestion was the commonest mode of poisoning (97.2%). Pesticides constituted the highest percent among cases, where aluminum phosphide was the most prevalent agent of poisoning. According to PSS (53%) of cases were moderate versus 45.3% were severe. Survivors were (57.5%), while non-survivors were (42.5%). Significantly lower PH, Hco3, PaO2, oxygen saturation, serum potassium levels, and much lower values of BD (more minus results) in the non-survivors, while serum creatinine was significantly higher in the non-survivors. From the ROC curves, patients were considered of a bad prognosis when Ph ≤ 7.24, Hco3 ≤14.55, BD ≤ -5.6, Pao2 ≤ 31.6, and K ≤3.62 (p-value <0.001). CONCLUSION: It is a cornerstone to assess the acid-base and electrolytes disturbances, especially base deficit and Hco3 level for helpful prediction of the outcome, and categorization of the cases who need ICU admission from the start even if they are asymptomatic.