- Observatoire aquitain des sciences de l'univers
- Observatoire régional de la santé
- Occupational and Environmental Epidemiology Branch [Bethesda, Maryland]
- Ochsner Clinical School
- Oenologie
- OK5, Center for Medical Genetics,
- Okairos
- Oncogenetics Laboratory
- Onekin [Donostia]
- Ontario Cancer Genetics Network
- Ontario Institute for Cancer Research [Canada]
- Open Research Center for Lipid Nutrition
- Optimisation des régulations physiologiques
- Optimisation thérapeutique en Neuropsychopharmacologie
- Orange Labs [Cesson-Sévigné]
- Orgamétrie biostatistiques
- Orpéa|Clinéa
- ORS PACA, Southeastern Health Regional Observatory, Marseille, France
- Ospedale Niguarda
- Osyris SA
- Oxford Centre for Diabetes, Endocrinology and Metabolism
- Oxylipides