The emergence of neurosurgery from the practice of cranial surgery between the eighteenth and the twentieth centuries in London, UK, is well documented, including the role of Sir Victor Horsley, the first neurosurgical appointee at the National Hospital Queen Square in 1886. The process of this transition elsewhere in London and the subsequent foundation of other neurosurgical units are less well described. In East London, the status of St. Bartholomew's Hospital (Barts) as the oldest London hospital still active on its original site and its comprehensive archives allow an unusually long history of surgical practice in the specialty to be studied. Using these archives and other primary and secondary sources, this article describes the transition of cranial surgery in East London from the general surgeons, limited to the treatment of brain and skull injury, to the specialized discipline of neurosurgery. We discuss the culmination of this process in the foundation of three neurosurgical units at London Hospital, Whitechapel, by Sir Hugh B. Cairns from 1927; at Barts Hospital, Smithfield, by John E. A. O'Connell from 1937; and at Oldchurch Hospital, Romford, by Leslie C. Oliver from 1945. Two modern neurosurgical units, in Whitechapel and Romford, have taken forward the work begun by this group.