- Ochsner, Albert J. (Albert John), 1858-1925, author2
- Ohmann-Dumesnil, A. H. (Amant Henry), 1857-1919 author12
- Oliver, Charles A. (Charles Augustus), 1853-1911 author5
- Osborn, Henry Fairfield, 1857-1935, author1
- Osler, William, Sir, 1849-19191
- Osler, William, Sir, 1849-1919, author1