- Optimal Care Inc.
- Optimal Home Care
- Option Care
- Option Care Health
- Option Health Care
- Options Home Care
- Optum
- Optum Healthcare
- Optum Public Sector Solutions
- Optum Ventures
- OptumCare
- Opus
- Oracle
- Oregon Association for Home Care
- Oregon Hospice and Palliative Care Association
- Oregon Non-Profit Hospice Alliance
- Organization of Nurse Leaders of Massachusetts & Rhode Island
- Orlando Health
- Orthomed Appliance Inc.
- Osborne Home Care Group