Myofibroma of the muscle is extremely rare. This report describes a 46-year-old man with myofibroma of the left supraspinous muscle on 18F-FDG PET/CT and includes MRI and 18F-FDG PET/CT findings. Whole-body 18F-FDG PET/CT showed abnormal tracer uptakes in the left supraspinous muscle, which was subsequently confirmed as myofibroma by histopathology.