[What does the Babinski sign have to offer 100 years after its description?].

One hundred years after its description, the Babinski sign remains a faithful and precise indicator of dysfunction in the pyramidal tract. Unlike a normal plantar reflex, which is a local reflex (S1), the Babinski sign is an integral part, though with its own specificity and thus value, of the defense reflectivity of the lower limbs. It should be triggered, preferably in the lateral region of the foot, by a non-painful stimulation. The characteristic response is a dorsal flexion of the greater toe by recruitment of the extensor hallucis. The pathological response is related to a dysfunction involving a precise fraction of the pyramidal tract (van Gijn. 1996), responsible for a monosynaptic stimulation of the extensor hallucis motor neurons, but also, via interneurons, for inhibition of the extensor hallucis. Its relationship with defense reflexes is certain (Walshe, etc.) put quite complex. We refer here to the "fanning" sign or Babinski "equivalents", plantar areflexia, peripheral "pseudo-Babinski", responses obtained by stimulating the plantar aspect of the foot in the newborn, and to global hyperflexion. We also discuss the role of the Lundberf dorsal reticulospinal tract.