Rheumatic fever (RF) is a significant public health problem in underdeveloped countries, and its diagnosis is based on modified Jones criteria. However, there are rare manifestations not included in these criteria that can complicate this condition. We present a case report of a 21-year-old Moroccan female with RF revealed by pulmonary involvement. The patient had no known rheumatic fever. She presented with a two-week history of joint pain, severe chest pain, and shortness of breath. On clinical examination, she was febrile with a palpable left knee joint effusion. Laboratory tests indicated elevated levels of inflammation markers and moderate hepatic cytolysis. The thoracic CT scan revealed extensive bilateral alveolar-interstitial parenchymal involvement. The left knee joint puncture showed an inflammatory fluid without germs or microcrystals. Antibiotic therapy with ceftriaxone and gentamycin was ineffective. Echocardiography revealed rheumatic poly valvulopathy with mitral valve narrowing and moderate to severe mitral insufficiency. Streptolysin O antibody levels were high. The diagnosis of RF complicated by rheumatic pneumonia was made. Treatment with amoxicillin and prednisone led to favorable outcomes.