Background: Acute theophylline toxicity represents a significant hazard, mainly in developing countries, due to its severe consequences, the absence of an antidote, and the existence of many factors that affect the prognosis of acutely theophylline-intoxicated patients. Aim: This study aimed to investigate the role of glucose/potassium ratio in the early prediction of the severity and outcome of acute theophylline toxicity in terms of morbidity and mortality, compared to serum theophylline concentration as the gold standard predictor. Methods: This cross-sectional study was conducted on adult patients with a diagnosis of acute theophylline toxicity admitted to the Poison Control Center, Ain Shams University hospitals, during the period from the beginning of January 2021 to the end of June 2022. For each patient, sociodemographic, clinical, and laboratory data, including theophylline levels and glucose/potassium ratio, were recorded. Results: Fifty-seven patients were enrolled in the study and classified according to the Poisoning Severity Score into minor, moderate, and severe toxicity groups. Both theophylline levels and glucose/potassium ratios were significantly higher in the severe and moderate groups compared to the minor group, and both predicted severe cases. However, theophylline level was more specific, while the glucose/potassium ratio was more sensitive for predicting severe cases. Conclusion: A high glucose/potassium ratio can be used for the early prediction of severe cases of acute theophylline toxicity