Septic arthritis of acromioclavicular (AC) joint is a rare entity. It is generally seen in patients who are immunocompromised. Only 15 cases have been reported till now, with only one case series of 6 patients. We report a case of septic arthritis of AC joint in an immunocompetent child. A 9 years old girl presented with history of pain in left shoulder for 4 days associated with fever. No history suggestive of any immunocompromised state was complained. On local examination, a swelling of around 3 cm in diameter was found over left AC joint region with raised local temperature, tendess on palpation and positive response in fluctuation test. Total leukocyte count was 18.7 × 109/L with 80％ of neutrophils. Erythrocyte sedimentation rate (ESR) was 28 mm/1 h. C-reactive protein (CRP) was 12 mg/L X-ray showed enlarged left AC joint space. Ultrasound revealed hypoechoic collection in the AC joint and the surrounding area. The aspirate was thick and purulent in nature, revealing Gram positive cocci at staining. Arthrotomy and thorough lavage of AC joint was done. Culture of the aspirate showed Methicillin Resistant Staphylococcus Aureus (MRSA) after 48 hours that was sensitive to amikacin, gentamicin, erythromycin and teicoplanin. Patient was symptom-free at 2 months of follow-up with no signs of osteomyelitis on the radiographs. Thus this is the first case of AC joint septic arthritis in healthy individual. Being proximal to the shoulder joint, AC joint septic arthritis can be confused with the shoulder joint septic arthritis. Thus, high index of suspicion is required for accurate diagnosis.