Ludwig Mauthner was only 19 years old when he published his discovery of the colossal fibers in the spinal cord of fishes which now bear his name. Based on Mauthner's works, archival material, and contemporary sources we provide a summary of his life and work as neuroanatomist and ophthalmologist in imperial Austria. In the years 1859-1863 Mauthner published four papers on the structure of the central nervous system in vertebrates. His first report on fishes contains the original description of a 'colossal myelinated nerve fiber' on each side of the central canal, extending through the entire spinal cord. Another, more general, treatise on 'the morphological elements of the nervous system' (published in 1863) summarizes his neurohistological studies of various vertebrates. It includes a classification of nerve cells based on their (histochemical) reaction to carmine. The main findings were soon shown to be artefactual; the paper had a long-range impact, however, because it provoked fruitful controversy among contemporary neuroanatomists. Mauthner published several monographs and numerous articles in ophthalmology, a newly developing branch of medicine that he chose for his later career. After abruptly resigning from a professorship at Innsbruck University, he opened a private practice in Vienna and continued lecturing in his field. He became a noted eye-surgeon, was elected Assistant Director of the Vienna 'Allgemeine Poliklinik', and in 1894 became Professor and Chair of Ophthalmology at the University of Vienna. Mauthner unexpectedly died on the night following the formal announcement of his appointment.