Pembrolizumab, one of many novel immune checkpoint inhibitors (ICPi), is a monoclonal antibody that enhances immunity against cancer cells. Extensive escalation in immune activity predisposes to unsought immune-related adverse events. Due to progressive mesothelioma, a 67-year-old man was referred to the research unit and enrolled in a clinical trial with a cluster of differentiation (CD) 27 chemotherapeutic agent. He began crossover treatment and received just two doses of pembrolizumab, 33 and 16 days prior to admission. He subsequently presented to the emergency department with three days of acute onset severe diplopia and a drooping left eye. Acetylcholine receptor (AChR) antibodies returned positive at 13.9 nmol/L, and a diagnosis of ocular myasthenia gravis (OMG) was made. During his hospitalization, the patient was managed with methylprednisolone 80 mg intravenously daily, with conversion to prednisone 60 mg by mouth daily at time of discharge. Neuro-ophthalmology consultation was sought in the outpatient setting, and the patient was started on pyridostigmine. He was readmitted two weeks later with symptoms of progressive diffuse weakness, unsteady gait, and dysphagia, all in the setting of persistent diplopia. Intravenous immunoglobulin (IVIG) was promptly initiated, in addition to the pyridostigmine previously initiated in the outpatient setting. Unfortunately, after three IVIG treatments, the patient had experienced little improvement in his symptoms, and therefore elected hospice care. Although ICPis have revolutionized the management of a multitude of malignancies, recognition of immune-related adverse events is of critical importance.