& aim: Acute rheumatic fever is an autoimmune disease that mainly affects the large joints. Early treatment of a throat infection following group A streptococcus prevents of acute rheumatic fever. Given the low prevalence of the disease, especially in a situation where there is excessive use of antibiotics in Iran, this study intends to report a patient with acute rheumatic fever with mild criteria. Case report: the patient was a 14-year-old male that came to the internal medicine clinic due to

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... weakness and joint pain. The patient had pain in the joints of the wrists and ankles, as well as the knees which was migratory in the patient. He had a history of fever and sore throat a month before the visit. The patient did not describe the skin lesion. On examination, the patient had vital signs of BP: 100/60 mmhg, PR: 90 / min, RR: 25, and T: 37.7. The throat examination was slightly erythematous, and without exudates, the cardiac examination was tachycardia without murmur. On examination of the joints, only the left knee joint had redness, and it was warm to the touch. In the laboratory tests, ASO: 400, ESR: 94 and CRP: 76 were. The patientchr('39')s chest x ray, ECG, and echocardiogram were normal. Based on the symptoms and laboratory tests in Jones criteria, the diagnosis of ARF was confirmed. Then, the initial treatment, naproxen and co-amoxiclav was started, and explained for the patient to receive injection of penicillin benzathine once a month until the age of 21. Conclusion: Acute rheumatic fever should be considered as part of the differential diagnosis of polyarthritis in the young patients, so that, if present, with appropriate treatment and prophylaxis, we can to able reduce the social costs from rheumatic heart disease.