- O'Melveny & Myers
- O&M Investments
- O&M Investments LLC
- Oak Brook Healthcare Centre
- Oak Street Health
- Oak Trace
- Oakridge Gardens Nursing Center
- Oakview
- Obamacare
- Occupancy
- Occupational Safety and Health Administration
- Ocean Healthcare
- Ocean Healthcare Group
- Ocean Healthcare Network
- Ochsner Clinic Foundation
- Ochsner Health System
- OCR
- Odd Fellow Home
- Odin Health & Rehab Center
- Office of Inspector General