Pulmonary sequestration (PS) is a rare congenital bronchopulmonary malformation characterized by nonfunctional lung tissue lacking communication with the tracheobronchial tree and a receiving systemic arterial supply. Intralobar sequestration (ILS), the most common subtype, is usually diagnosed during childhood or early adulthood and is rarely identified after the age of 50. ILS usually manifests with hemoptysis or recurrent pulmonary infection. We report the case of a 53-year-old woman with a history of rheumatic mitral regurgitation and rheumatoid arthritis treated with methotrexate and corticosteroids, who presented with mild exertional dyspnea and constitutional deterioration. Pulmonary function tests showed preserved ventilatory function and normal diffusing capacity, with no exercise-induced desaturation. Chest computed tomography revealed cystic lesions in the left lower lobe supplied by an aberrant artery arising from the descending thoracic aorta, consistent with intralobar pulmonary sequestration. This case highlights an unusual late diagnosis of ILS in a patient with autoimmune disease and emphasizes the diagnostic value of contrast-enhanced computed tomography as well as the importance of individualized therapeutic decision-making.