A 5-year-old boy was admitted to the hospital with a high fever and abnormal gait. Magnetic resonance imaging showed extensive swelling of the quadriceps and adductor muscles around the right hip and anterior thigh. A duplex scan demonstrated a thrombus from the external iliac vein to below the popliteal vein. The blood culture revealed Streptococcus pyogenes. The patient was immediately treated with antibiotics and anticoagulants. Follow-up sonography demonstrated complete disappearance of the venous thrombosis. We report a case of streptococcal myositis complicated by deep vein thrombosis.