Abstract Disclosure: G. Wintermyer: None. C. Arcilla: None. E. Villanueva: None. Autoimmune polyglandular syndrome type II (APS II) is a rare combination of multiple endocrine diseases. The most common associated diseases are diabetes type I, Hashimoto thyroiditis, and Addison’s disease. Most patients present with nonspecific symptoms, typically in adulthood. Here we describe a 19-year-old female with APS II:A 19-year-old female with history of depression presented to hospital with severe nausea, vomiting and chest pain. She was diagnosed with pneumomediastinum secondary to hyperemesis. The symptoms were assumed secondary to ziprasidone that she was then taking.Patient experienced 20-pound weight loss in a very short period. Patient went to ED again for excessive weight loss. She was diagnosed with DKA for the first time and was admitted to ICU (Glucose level above 500 mg/dL and A1C 7.1%). After discharge, patient came to the endocrinology clinic for management of type 1 diabetes. Her BMI was 17 kg/m2. Vital signs were normal. Since the start of insulin therapy, patient gained weight and her BMI increased to 18.5 kg/m2.Patient was clinically well for about 1 year. She had periodic complete blood tests, including TSH, A1C and CMP, all of which remained normal with A1C’s of 6.3% and 6.8%. Approximately 1 year later, her TSH was 8.230 uIU/mL and free T4 was 0.92 ng/dL with subsequent TPO of 27 IU/mL. Diagnosis of Hashimoto’s hypothyroidism was made, and she was started on levothyroxine.Even though patient was on treatment for hypothyroidism, she complained of fatigue. CMP showed sodium 133 mEq/l and bicarbonate 17 mEq/l. Celiac antibodies presented negative. Cortisol AM and ANA were ordered. Before patient had the lab tests done, she was admitted to psychiatric hospital due to psychosis and bizarre behavior. Shortly after, patient was transferred to medical hospital for nausea and vomiting. Her labs were as follow: Sodium 100 mEq/l, Potassium 6.5 mEq/l, Bicarbonate 12 mEq/l, anion gap 19, Glucose 157 mg/dl. Stat cortisol and ACTH were 1.3 mg/dL and 332 pg/mL, respectively.Patient was admitted to ICU with adrenal crisis. She was started on Fludrocortisone and IV Hydrocortisone and IV fluid for hyponatremia. She was discharged from hospital with resolution of her psychiatric features. Her final diagnosis was APS II. She was started on Fludrocortisone 0.1, Hydrocortisone 20 mg in the morning and 10 mg at night.Clinicians should keep this disease in mind when assessing a patient who has presented with other autoimmune endocrinologic diseases, especially diabetes type I or adrenal insufficiency. Frequent visits, vital checks, CMP, and antibody screening tests including GAD antibodies, anti-adrenal antibodies, and TPO antibodies help in diagnosing this syndrome earlier.Clinicians also should be mindful of psychiatric features in a patient. They should try to rule out medical causes before diagnosing a patient with psychiatric disease as profound hyponatremia can cause acute psychosis. Presentation: Saturday, June 17, 2023