Joseph Babiński pioneered development of French neurosurgery and world clinical neurology. Although he was best known for his discovery of the extensor plantar response, his foundations in the modern semiology of neurology are unequivocal. He introduced the concepts and terminology of cerebellar symptoms and discovered a reflex asymmetry as the sign of organic disease. Although he considered the development of French neurosurgery by his pupils as his greatest accomplishment, it is 'the sign' that has dominated his legacy over the years. This sign will also celebrate a centenary in 1996.