Abstract Background Rare causes of secondary hypertension should be considered after negative initial evaluation for more common conditions. 11-Deoxycorticosterone-secreting tumors are one such rare cause. Clinical Case A 38-year-old male with two-year history of resistant hypertension on four antihypertensive medications (amlodipine, hydrochlorothiazide, lisinopril, spironolactone) presented to the emergency room with one-day history of headaches and hypertension. Initial vitals were blood pressure of 179/117, heart rate 68, respiratory rate 18, and SpO2 of 100% on room air. Labs were notable for hypokalemia of 2.2, normal creatinine of 1.03, and troponin elevation of 0.08. EKG showed no ischemic changes. During the hospital admission, spironolactone dose was increased, amiloride was added, hydrochlorothiazide was discontinued, and potassium was supplemented. The patient's blood pressure stabilized, and troponin normalized. Evaluation for secondary causes was also initiated, including plasma renin, aldosterone, and metanephrines, with results pending on discharge. Outpatient CT abdomen and pelvis was also ordered. The patient was discharged on the third day of admission on an increased dose of spironolactone 100mg daily, amiloride 5mg daily, amlodipine 10mg daily, lisinopril 40mg daily, and potassium 20meq twice daily. Laboratory studies and outpatient endocrinology evaluation revealed suppressed plasma renin activity 0.1 ng/mL/hr, low aldosterone <3.0 ng/dL, elevated 11-deoxycorticosterone (DOC) 869 ng/dL (reference range ≤19 ng/dL), and elevated 11-deoxycortisol 719 ng/dL (reference range ≤49 ng/dL). Plasma and urine metanephrines, 24-hour urinary free cortisol, and plasma DHEAS were normal. CT revealed a large 9.7×10.0×10.7cm heterogeneously enhancing right adrenal mass and several subcentimeter bilateral pulmonary nodules. FDG PET-CT showed mild heterogeneous uptake of the adrenal mass with SUVmax of 5.1 and hepatic SUVmean of 2.5, without convincing metabolic evidence of metastasis. Mild uptake was noted in the mediastinal, hilar and left axillary lymph nodes, which were not suspiciously hypermetabolic and favored to be reactive, perhaps related to recent COVID-19 vaccination administered to the left upper extremity. The subcentimeter pulmonary nodules did not have increased avidity. The patient underwent open right adrenalectomy without complications. Pathology revealed 11.5cm low-grade adrenocortical carcinoma with clear margins and angioinvasion, Ki67 proliferation index of 1-2%, and without necrosis, lymphovascular invasion, or extra-adrenal extension. 11-deoxycortisol normalized and DOC was undetectable at one and three months postoperatively. Blood pressure improved significantly, and all antihypertensives were discontinued except amlodipine 10mg daily. On surveillance CT scan six months after surgery, there was no evidence of residual disease in the adrenalectomy bed and pulmonary nodules appeared stable. Conclusions Adrenocortical carcinomas rarely produce aldosterone and even less commonly produce DOC as the major steroid product. DOC should be evaluated in the setting of hypertension with hypokalemia, suppressed renin and aldosterone. Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m.