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We report a case of a 37-years-old female that presented with a three-week history of diplopia, ptosis, muscle weakness, difficulty chewing, tachycardia, and fatigue; these clinical symptoms were concerning for acute myasthenia gravis crisis. The diagnosis of Myasthenia gravis was further confirmed by a positive immunology workup. Chest CT imaging during her assessment showed anterior mediastinal mass/enlarged thymus indicative of thymic hyperplasia. Medical therapy with intravenous immune globulin, pyridostigmine and further treatment with high-dose steroid. She had a positive response to treatment but still reported persistent symptoms of fatigue, tachycardia, and intermittent diplopia, raising suspicions for underlying Graves’ thyrotoxicosis. Thyroid function testing was performed which showed a very suppressed thyroid-stimulating hormone (TSH) and elevated Free t4 levels. Further workup for Graves thyroid autoimmune antibodies indicative of extremely elevated thyroid stimulating hormone receptor autoantibodies consistent with Graves’ disease. We initiated medical therapy for Graves’ disease with a beta-blocker and thioamide (methimazole). She endorsed progressive improvement in her symptoms following treatment for Grave's disease. She was discharged with high dose steroids, pyridostigmine, and appropriate therapy for Graves’ disease. She did well after her discharge from the hospital and six months afterwards she returned to the hospital for a robot-assisted right thymectomy. Final pathology report indicative of non-thymomatous myasthenia gravis. She continued to follow up with us in the endocrinology outpatient clinic. Her steroid therapy was tapered off and medical therapy for Graves’ disease was continued accordingly. She demonstrated a positive response to medical therapy with remarkable improvement in the remaining of her symptoms, especially her neurological and ocular symptoms after initiation of treatment for Graves’ disease. Conclusion we report two rare concomitant autoimmune diseases, myasthenia gravis, and Graves’ disease. Both conditions have similar overlapping clinical features making diagnosis and treatment challenging in clinical practice. It is well reported in clinical literature and studies that hyperthyroidism may worsen symptoms of MG and management of hyperthyroidism in the setting of MG may lead to worsening of myasthenia symptoms; hence, certain precautions should be taken to avoid worsening symptoms of myasthenia gravis. Therefore, we call for more case-control, case series and clinical trials to explore more clinical knowledge about the association between the two conditions and formulate better management strategies. Presentation: Sunday, June 12, 2022 12:30 p.m. - 2:30 p.m.