The presentation of affective disorders and psychosis in the context of hyperthyroidism is very rare. We present the case of a 65-year-old patient who presented an intense fear of the new coronavirus disease (COVID-19), depressed mood, anxious, nihilistic delusions, guilt, somatic and apathy. He was diagnosed with a major depressive disorder with psychosis which developed Cotard's syndrome in addition to having Graves-Basedow disease. Treatment consisted of venlafaxine 150 mg/day, quetiapine 50 mg/day, thiamazole 30 mg/day, and propranolol 60 mg/day. After two weeks of treatment, the patient improved and was discharged. The article is complemented with a literature review on the association between mental symptoms, Cotard's syndrome and hyperthyroidism.