The Sir William Osler Collection, distinct from the Bibliotheca, is an extensive archival holding of Osler's correspondence (including eighteen hundred original letters), daybooks, accounts, engagement books, legal documents, book invoices, membership certificates, notebooks, lectures, addresses, newspaper clippings, photographs, books with manuscript additions, and miscellaneous loose items formerly inserted into individual books in his library. The collection also contains various family papers, including correspondence of Lady Grace Revere Osler and Edward Revere Osler.

Fonds contains correspondence mostly between George Dock and Sir William Osler but also with Lady Osler, W.W. Francis and Archibald Malloch, from 1891 to 1919. The fonds includes 106 letters, originals and carbon copies.

Fonds documents Burton Chance's links with Casey A. Wood from 1922 until Wood's death in 1942. The fonds contains correspondence between the two men, reprints of C.A. Wood and letters from various correspondents concerning C.A. Wood.

The fonds contains materials that Dr. M. Entin collected for his biography of Dr. Archibald. Mainly include articles relate to tuberculosis, pancreatitis, wound healing, history of surgery, and scientific writing. It also includes letters from Edward Archibald to Mrs. Archibald, letters to Archibald from William Osler and Sir Henry Gray, addenda of Archibald's world journey in 1936, and articles by Archibald.

Some draft chapters of the biography of Dr. Archibald and research data for 100th Anniversary of Royal Victoria Hospital can also be found in the fonds.

The fonds contains correspondence related to the Osler Library and its holdings with people such as Maude Abbott, Edward Archibald, William B. Bean, Edward Horton Bensley, Archibald Malloch, Casey Wood, as well as John Farquhar Fulton, Keeper of the Medical History Collections at Yale University's library; the fonds also contains a typescript of talks by W.W. Francis (titled "Showman's Patter") about books and other items held in the Osler Library.

Series D contains correspondence concerning topics of Dr. Elliott’s professional interest.
This series is divided into two (2) sub-series:
D/1) Correspondence, 1944-1986
D/2) General correspondence, 1936-1985

Fonds contains G.E. Tremble's notes on the anatomy of the ear from lectures by Professor Ruttin at the University of Edinburgh in 1924, a letter from Dr. Wilder Penfield and a photograph of a case of 1935. The fonds includes a notebook, a letter and a photograph.

The fonds contains Margaret Gillett's source materials and drafts for her book Dear Grace, a Romance of History. The source materials include original letters from William C. Little to Grace Ritchie written between 1889-1893.

The fonds documents mainly Babkin's professional interests in physiology, especially glandular secretions and the nervous system. The fonds contains correspondence; lecture notes; citations; research notes and papers, including manuscripts sent to him by his colleagues; reprints of scientific articles mainly in Russian; and material used in the preparation of the biography of Ivan Pavlov. The latter contains correspondence with Ivan Petrovich Pavlov and members of his family, 1923-1948; photographs and portraits; and an unabridged typescript copy of Parts 1-3 of Pavlov: a Biography, with manuscript corrections, 1943-1946.

Fonds consists of pamphlet entitled, “What to Eat to be Healthy” (Toronto: Canadian Medical Association and Canadian Life Insurance Officers Association, 1937), authored by Tisdall. Fonds also includes: typed letter signed from J. P. Crozer Griffith to Tisdall, Feb. 10, 1923, concerning a case on which Tisdall had consulted Griffith; autographed letter signed from Mrs. J. B. Gregory and Eliza J. Gregory, Aug. 2, 1920, agreeing to lease rental property to Tisdall; and autographed receipt signed from Mrs. J. B. Gregory acknowledging receipt of Tisdall’s rental payments.