Atezolizumab is a monoclonal antibody that targets programmed death ligand-1. Treatments with this drug may cause immune-related adverse events by creating an exaggerated inflammatory response. The most common side effects are fatigue, rash, and gastrointestinal symptoms. Cases of central nervous system toxicity such as encephalitis and encephalopathy are uncommon. We present the case of a 53-year-old female with metastatic squamous cell carcinoma of the cervix who presented to the emergency room 13 days after receiving atezolizumab with altered mental status, headache, and meningeal signs. She was admitted to the intensive care unit. Infectious, anatomical, and neoplastic etiologies were ruled out. Auto-immune meningoencephalitis was diagnosed and treated with high-dose steroids. Within 10 days of the diagnosis, she had clinical, radiological, and laboratory improvement. Given the increasing use of novel immunotherapies and life-threatening side effects associated with them, healthcare providers in the intensive care unit should be aware of their diagnosis and management.