He later wrote "There was no infirmary in Edinburgh when I served my apprenticeship there, so that I never had an opportunity of seeing a cancerous breast extirpated or any other capital operation performed till I performed them myself." The first teaching hospital (the "Little House") opened opposite the head of Robertsons Close on 6 July 1729. Hill joined the Royal Navy as a surgeon in 1730. At this time naval surgeons were certified for the purpose after an examination by the Court of Examiners of the London Company of Barbers and Surgeons and many naval surgeons of the day had no other formal qualifications. Surgical practice in Dumfries
In 1732 Hill returned to Dumfries where he set up in surgical practice. On 28 January 1733 he married Anne McCartney, whose father John owned the Blacket (or Blaiket) estate, in the Parish of Urr and it was there that they established the family home. His practice was conducted from his town house in Amisfields Lodging in the Fleshmarket, in Dumfries. There is no known portrait of James Hill but Murray provides this description: "... his height being about five feet eleven inches. He continued till his death to prefer that fashion of dress that had prevailed in his youth. He wore a full wig ; and used a large staff. He was a man of dignity both of appearance and manners." Between 1742 and 1775,  Hill trained sixteen surgical apprentices.
Head injuries, he asserts, have been treated in ‘a much more rational manner’ in the previous 15 years as a result of discoveries and ‘valuable publications’ over that period. He describes the rationale for his treatment and how this changed over time as his knowledge and understanding of the problems progressively increased. He gives ‘a historical view of the gradual progress of the improvements made by others as well as by myself.’
His first patient, a five-year-old boy, sustained a depressed frontal fracture associated with an epidural haematoma (EDH). When the fracture was elevated and the haematoma drained by trepanning the skull, the boy ‘immediately recovered his senses’ but after some days the ‘stupor’ returned, indicating that some matter was lodged under the meninges’. Hill made a cruciate incision in the meninges to drain the haematoma with beneficial effect. Ganz regarded this as the first ever description of a lucid interval associated with a subdural haematoma. This case also demonstrates Hills understanding of the clinical features of cerebral compression: ‘The smallest compression brought on a stupor, a low intermittent pulse, nausea, vomiting and sometimes convulsive twitches.’ From case 3 onwards he avoided dressings which compressed the trepanned area. In case 3 he again relieved the features of cerebral compression by a trepan with drainage of an EDH. In case 5 drainage of a large EDH resulted in restoration of consciousness and resolution of a right sided weakness.