Andrew Taylor Still, MD, DO, coined the original idea of lesion based on the obstruction of flow of body fluids, but primarily referring to bony structures and more precisely to the spine. Throughout the 20th century, this idea was shaped and developed into the concept of somatic dysfunction, a term that is familiar to both US-trained osteopathic physicians and foreign-trained osteopaths and has been an essential cornerstone of osteopathic practice and teaching. The present historical narrative review offers an overview of the evolution of Still's original lesion concept, major evidence-based models of somatic dysfunction that attempt to explain the clinical findings, and a critique of the concept.