Streptococcal myositis is a rare, often fatal, acute infection of the muscle, caused by an invasive groupA β-haemolytic streptococcus. It is characterised by muscle necrosis without abscess formation, and in contrast to necrotising fasciitis, does not primarily affect the subcutaneous tissue or skin. A young adult male presented with streptococcal myositis initially affecting the rectus femoris muscle of his left thigh. The symptoms, signs and management are discussed. Particular emphasis is given to the benefits of emergency CT scans to diagnose and delineate the extent of the disease. These scans may need to be repeated if the disease progresses. The four cornerstones of management are: early diagnosis using emergency CT scans; high-dose intravenous antibiotics; early aggressive surgical debridement; and intensive fluid and nutritional support.