The Hydrocephalus Association supports individuals affected by hydrocephalus through research funding, community resources, and advocacy efforts.

Hydrocephalus Canada supports individuals and families impacted by spina bifida and hydrocephalus, providing resources, advocacy, and emotional support.

The Hyper IgM Foundation is a non-profit organization dedicated to improving the treatment, quality of life, and long-term outlook for children and adults living with Hyper IgM Syndrome through research, support, education, and advocacy.

The Hypermobility Syndromes Association supports individuals with symptomatic hypermobility by providing management-focused patient support groups, educational programs, and advice for both patients and healthcare professionals.

The Hypersomnia Foundation supports individuals with idiopathic hypersomnia and related sleep disorders by providing resources, education, and a community for those affected.

The Hypertrophic Cardiomyopathy Association (HCMA) provides support, education, and advocacy for individuals affected by Hypertrophic Cardiomyopathy (HCM), a common genetic heart disorder.

The HypoPARAthyroidism Association is a non-profit organization dedicated to improving the lives of individuals affected by hypoPARAthyroidism through education, support, research, and advocacy.

I AM ALS is a non-profit organization that empowers people living with ALS, supports their families, and advocates for research and policy change to improve lives and find a cure.

The IgA Nephropathy Foundation is dedicated to supporting individuals affected by IgA Nephropathy through patient advocacy, funding research, and providing resources for better treatment options.

INAD Warriors, Inc. is dedicated to raising awareness and funding research for infantile neuroaxonal dystrophy (INAD) and related PLA2G6 gene disorders, while supporting families affected by this ultra-rare disease.

The INADcure Foundation is a nonprofit organization dedicated to funding research and raising awareness for Infantile Neuroaxonal Dystrophy (INAD) and other related neurodegenerative diseases, while providing support to affected families.

The ITP Support Association is a UK charity that supports patients and families affected by Immune Thrombocytopenia (ITP) by providing information, support, and funding for research and medical education.

The IgG4ward! Foundation provides support, education, and advocacy for individuals affected by IgG4-related disease (IgG4-RD), a rare immune-mediated disorder.

The Ileostomy and Internal Pouch Association (IA) is a registered charity that supports individuals living with an ileostomy or internal pouch, providing resources, information, and one-to-one support for patients and their families.

The organization supports patients with rare diseases through various services, including medical rehabilitation, education, and advocacy efforts.

The Immune Deficiency Foundation supports patients and families affected by primary immunodeficiency diseases, including DiGeorge syndrome and 22q11.2 deletion syndrome.

Immunize.org provides resources and information about vaccines for healthcare professionals and the public, focusing on improving vaccination rates and understanding of immunization.

The Indian Health Service provides health care services to American Indians and Alaska Natives, focusing on public health responses and partnerships with tribal organizations.