BACKGROUND Cardiac tamponade is a life-threatening pericardial compressive disorder that is a common downstream manifestation of infections, malignancy, and metabolic disorders. Hypothyroidism is a rare cause of tamponade that is attributed to the slow accumulation of effusive fluid into the intrapericardial space. In individuals living with HIV/AIDS, tamponade is commonly associated with infection or malignancy. To our knowledge, this is the first reported case of a patient with HIV/AIDS to have been identified with tamponade secondary to hypothyroidism. CASE REPORT Herein, we describe the case of a 52-year-old male patient with a history of AIDS, who presented with nausea, vomiting, diarrhea, and episodic gastrointestinal discomfort for the past several weeks, in conjunction with progressive fatigue. At initial presentation, he had no hemodynamic or clinical signs of tamponade, but pericardial effusion was incidentally found on imaging. Further investigations revealed an undiagnosed Hashimoto's thyroiditis as a function of restored immunocompetency, which ultimately led to the impending tamponade in this patient. We describe his clinical course through diagnosis of autoimmune hypothyroidism, review cardiac tamponade and hypothyroidism in the context of people living with HIV/AIDS, and discuss this rare manifestation of restored immunocompetency. CONCLUSIONS Hypothyroidism should be ruled out in all patients presenting with pericardial effusions or cardiac tamponade, even in people living with HIV/AIDS or those with a history of immune deficiencies.