Austrian surgeon, teacher, and researcher who carried out important studies in the physiology of the thyroid gland and surgery of the central nervous system.

Eiselsberg studied medicine at Vienna, Würzburg, Zürich, and Paris. In 1884 he received his M.D. from Vienna, where he was a pupil of and assistant to the brilliant Viennese surgeon Theodor Billroth. He was professor of surgery at Utrecht (1893), Königsberg (1896), and Vienna (1901). In 1890 he made note of the frequent occurrence of tetany cramps after goiter operations and two years later produced tetany experimentally by removal of the parathyroid glands. He later studied thyroid cancer and did important work in pituitary surgery.

It was while he was a professor at Vienna that Eiselsberg achieved a reputation as the leader of neurosurgery in Austria. He was one of the founders of modern gastrointestinal surgery and the first surgeon in Europe to remove a spinal column tumor. He pioneered in brain surgery and also performed studies on streptococcic infections.

Eiselsberg received honorary degrees from universities at Athens, Budapest, Debrecen, Edinburgh, Geneva, Leiden, Paris, and Vienna.