The treatment of cancer is a rapidly evolving field. As more chemotherapeutic agents become available, reporting the side effects of these agents in clinical practice becomes increasingly important. Nivolumab is one of the chemotherapeutic agents commonly used for treatment of renal cell carcinoma, metastatic melanoma, and metastatic non-small cell lung cancer. While common side effects are known and well documented, encephalitis is documented as an extremely rare side effect. We present the case of an extremely rare side effect to a common chemotherapeutic agent.