| Obesity and depression in the enlightenment: the life and times of George Cheyne | NetLibrary |  NetLibrary |
| Obsessive compulsive anonymous: recovering from obsessive compulsive disorder | NetLibrary | NetLibrary |
| Obsessive-compulsive disorder: contemporary issues in treatment | NetLibrary | NetLibrary |
| Obstetrics: Normal and Problem Pregnancies, 5th ed., 2007 | MDConsult | |
| Occupational Outlook Handbook | US Department of Labor | |
| Official Congressional Directory | US Government Printing Office | Free |
| Operative Surgery Manual, 1st ed., 2003 | MDConsult | |
| Ophthalmology, 2nd ed., 2004 | MDConsult | |
| Opportunities in holistic health care careers | NetLibrary | NetLibrary |
| Opportunities in physician careers | NetLibrary | NetLibrary |
| Optimizing therapeutic development in diabetes | NetLibrary | NetLibrary |
| Organ procurement and transplantation: assessing current policies and the potential impact of the DHHS final rule | NetLibrary | NetLibrary |
| Organ transplants: making the most of your gift of life | NetLibrary | NetLibrary |
| Organization and Members/ National Academy of Sciences | National Academy of Sciences | |
| Organization of Services for Mental Health | World Health Organization | Free as of March 2004 |
| Osler Medical Handbook, 2nd ed., 2006 | MDConsult | |
| Otolaryngology--Head & Neck Surgery, 4th ed., 2005 | MDConsult | |
| Overload, performance incompetence, and regeneration in sport | NetLibrary | NetLibrary |
| Oxford English Dictionary | Oxford University Press | |
