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 primarily documents Armstrong’s social life. They consist overwhelmingly of correspondence for the period 1909-1933. Letters from his professional colleagues, such as Sir William Osler, F.J. Shepard, Edward Archibald, William J. Mayo and others in the Mayo Clinic, are concerned largely with personal greetings, association memberships, or Medical Faculty business, particularly honorary degrees. Armstrong's non-medical correspondents include Lord Beaverbrook, Lord Atholstan, Sir Hugh Allan, Arthur Meighen, George Foster and Herbert Symonds. Topics include politics, Armstrong's war work and honours, some medicals matters, and personal news. Appended to this main series are obituaries and letters of sympathy to Armstrong's widow (1933), six photographs, including one of Armstrong in an operating room, and admission cards and diplomas from Armstrong's student years.

The fonds consists of Dr. Bensley's research notes and correspondence, particularly in relation to his publication McGill Medical Luminaries.