Theophylline toxicity is a life-threatening toxidrome that can present to an emergency department. To ascertain an immediate provisional diagnosis in toxicology at the emergency department is very challenging, especially when the patient presents with altered mental status, because the clinical features of several toxidromes overlap. We report a case of survival of undiagnosed theophylline toxicity that required intubation for two days in the intensive care unit. This was the first case to have been reported from our department. Accurate diagnosis of a toxidrome by gaining adequate history and conducting a thorough physical examination and early serum toxicology screening, coupled with good knowledge of toxicology, will lead to better patient outcomes.