This organization focuses on women's health issues, providing information and resources related to various conditions such as menopause, pregnancy, and reproductive health.

The OMSLife Foundation raises awareness of Opsoclonus Myoclonus Syndrome, maintains a support network for caregivers, and funds research for a cure.

Orphanet is a resource dedicated to improving knowledge on rare diseases to enhance diagnosis, care, and treatment for patients, while providing high-quality information and ensuring equal access for all stakeholders.

This organization provides information and support for individuals affected by Primary Orthostatic Tremor (OT), a rare neurological movement disorder characterized by high frequency tremors in the legs when standing.

OMF is the leading resource for eye cancer research funding, education, and patient/caregiver support, focusing on ocular melanoma.

The Office of Minority Health works to improve the health of racial and ethnic minority populations and American Indians and Alaska Natives, focusing on eliminating health disparities.

The Oral Cancer Foundation is dedicated to reducing suffering and saving lives through prevention, education, research funding, advocacy, and patient support activities for oral and oropharyngeal cancers.

ORD India is a national umbrella organization advocating for the rights and resources of people with rare diseases in India, focusing on public awareness, policy development, and access to treatment.

O.U.C.H (Organization for the Understanding of Cluster Headaches) was a non-profit organization dedicated to advocating for and supporting individuals affected by cluster headaches, but it is no longer active.

The OI Foundation is the only voluntary national health organization dedicated to helping people cope with OI.

Ostomy Canada Society provides support, education, and resources for Canadians living with an ostomy, helping them to live life to the fullest.

Our Odyssey connects young adults impacted by rare or chronic conditions through accessible and inclusive social experiences.

Ovacome is the UK’s ovarian cancer support charity, providing personalized support and information to individuals affected by ovarian cancer since 1996.

The Oxalosis and Hyperoxaluria Foundation (OHF) supports individuals affected by hyperoxaluria through care, education, and research initiatives aimed at finding a cure.

PATH - Parents Available to Help, Inc provides resources, support, and information to families of children with special needs in Connecticut and beyond, offering services from prenatal to transition to adulthood.

PAVE provides support, training, information, and resources to empower individuals, youth, and families impacted by disabilities in Washington.

PBD Project is a non-profit organization focused on funding medical research to improve the clinical outcomes for patients with Peroxisome Biogenesis Disorders, particularly Zellweger Spectrum Disorder.

The PCD Foundation is dedicated to improving the lives of individuals with Primary Ciliary Dyskinesia (PCD) through education, advocacy, and support for research.