Louis-Stanislas Duménil (1823–1890) was a surgeon from Normandy who was a contemporary of Jean-Martin Charcot (1825–1893). Throughout his career, Duménil published annotated observations of neurological pathologies. One year before Guillaume Duchenne de Boulogne (1806–1875), he reported a case of “progressive muscular paralysis of the tongue, soft palate, and lips”. He added five other cases of progressive muscular atrophy in 1867, together with histological examinations which showed atrophy in the anterior horns of the spinal cord. Charcot, who described amyotrophic lateral sclerosis, did not fail to pay homage to Duménil for his contribution. In 1862, Duménil added clinical observations of progressive locomotor ataxia, one of the first to do so. This included anatomopathological examinations, thus significantly completing the clinical picture presented by Duchenne in 1858. He confirmed the damage to the roots and posterior tracts of the spinal cord. Finally, by providing multiple observations of the syndrome described by Octave Landry (1826–1865) in 1859, he contributed to the clinical picture of “acute ascending paralysis” which has come down to us as Guillain-Barré syndrome, with no mention of the perspicacious physicians of the previous century who had already perfectly recognised this disease. Finally, Augusta Dejerine-Klumpke (1859–1927) paid a warm tribute to Duménil in her 1889 thesis, calling him one of the pioneers in understanding “the individuality and autonomy of the peripheral nervous system.” He was indeed a pioneer, although he has been often overlooked.