- Old Bridge Medical Center
- Old Vineyard Behavioral Health Services
- Olean General Hospital
- Olive View - UCLA Medical Center
- Olivia Hospital & Clinic
- Olmsted Medical Center
- Olney Hamilton Hospital
- Olympic Medical Center
- Omega Hospital
- OneCore Health
- Oneida Health Hospital
- Onslow Memorial Hospital
- Ontario Hospital
- Ontario Medical Center
- Onvida Health
- Opelousas General Health System - Main Campus
- Optim Medical Center - Screven
- Optim Medical Center - Tattnall
- Options Behavioral Health Hospital
- Orange City Area Health System
- Orange Coast Medical Center
- Orange County - Anaheim Medical Center
- Orange County Global Medical Center
- Orange County - Irvine Medical Center
- Orchard Hospital
- Orchard Park Hospital
- Oregon State Hospital - Junction City
- Oregon State Hospital - Salem
- Orem Community Hospital
- Orlando Health Arnold Palmer Hospital for Children