See Rare Diseases by First Letter (A)
- Abdominal Aortic Aneurysm
- Abdominal Obesity Metabolic Syndrome
- Abetalipoproteinemia
- Abrikosov's Tumor
- Absent T Lymphocytes
- Acanthocheilonemiasis
- Acanthocytosis
- Acanthosis Nigricans
- Achalasia
- Achondroplasia
- Acinic Cell Carcinoma
- Acoustic Neuroma
- Acquired Fructose Intolerance
- Acquired Hemophilia
- Acquired Von Willebrand Syndrome
- Acral Lentiginous Melanoma
- Acromegaly
- Actinic Cheilitis
- Acute Articular Rheumatism
- Acute Biphenotypic Leukemia
- Acute Disseminated Encephalomyelitis
- Acute Erythroblastic Leukemia
- Acute Erythroid Leukemia
- Acute Graft Versus Host Disease
- Acute Intermittent Porphyria
- Acute Lymphoblastic Leukemia
- Acute Lymphoblastic Leukemia, Childhood
- Acute Megakaryoblastic Leukemia
- Acute Monoblastic Leukemia
- Acute Mountain Sickness
- Acute Myeloblastic Leukemia With Maturation
- Acute Myeloblastic Leukemia Without Maturation
- Acute Myelocytic Leukemia
- Acute Myeloid Leukemia, Adult
- Acute Myeloid Leukemia, Childhood
- Acute Myelomonocytic Leukemia
- Acute Non Lymphoblastic Leukemia
- Acute Promyelocytic Leukemia
- Acute Respiratory Distress Syndrome
- Addison's Disease
- Adenine Phosphoribosyltransferase Deficiency
- Adenocarcinoma of Lung
- Adenocarcinoma of the Appendix
- Adenoid Cystic Carcinoma
- Adenoma of the Adrenal Gland
- Adenomyosis
- Adenosine Deaminase Deficiency
- Adrenal Cancer
- Adrenocortical Carcinoma
- Adrenoleukodystrophy X-linked
- Adrenomyeloneuropathy
- Adult Neuronal Ceroid Lipofuscinosis
- Afibrinogenemia
- Aggressive NK Cell Leukemia
- Aicardi Syndrome
- AIDS Dementia Complex
- AL Amyloidosis
- Alagille Syndrome
- Albinism
- Albright's Hereditary Osteodystrophy
- Alkaptonuria
- Allergic Bronchopulmonary Aspergillosis
- Alpha 1-antitrypsin Deficiency
- Alpha-Thalassemia
- Alport Syndrome
- Alstrom Syndrome
- Alternating Hemiplegia of Childhood
- Alveolar Echinococcosis
- Alveolar Soft Part Sarcoma
- Alveolitis, Extrinsic Allergic
- Alzheimer Disease Familial
- Alzheimer Disease Type 2
- Amaurosis Fugax
- Amebiasis
- Amelogenesis Imperfecta
- Amyloid Neuropathy
- Amyloidosis AA
- Amyloidosis Cerebral
- Amyotrophic Lateral Sclerosis
- Anal Cancer
- Anaplastic Astrocytoma
- Anaplastic Ependymoma
- Anaplastic Large Cell Lymphoma
- Anaplastic Oligoastrocytoma
- Anaplastic Oligodendroglioma
- Anaplastic Plasmacytoma
- Ancylostomiasis
- Andersen-Tawil Syndrome
- Anencephaly
- Angelman Syndrome
- Angiofollicular Lymph Hyperplasia
- Angioimmunoblastic Lymphadenopathy With Dysproteinemia
- Angiomatous Lymphoid Hamartoma
- Aniridia
- Anodontia
- Anorectal Atresia
- Anterior Uveitis
- Anthrax
- Antiphospholipid Syndrome
- Antisocial Personality Disorder
- Antisynthetase Syndrome
- Aortic Coarctation
- Aortic Valve Stenosis
- Aphthous Stomatitis
- Aplasia Cutis Congenita
- Aplastic Anemia
- Apparent Mineralocorticoid Excess
- Apraxia
- Arachnoiditis
- Arginase Deficiency
- Argininosuccinic Aciduria
- Aromatic Amino Acid Decarboxylase Deficiency
- Arrhythmogenic Right Ventricular Dysplasia
- Arterial Calcification Due to CD73 Deficiency
- Arthrogryposis Multiplex Congenita
- Asbestosis
- Asherman's Syndrome
- Aspartylglycosaminuria
- Aspergillosis
- Asphyxia Neonatorum
- Ataxia Telangiectasia
- Atrial Myxoma, Familial
- Atrioventricular Septal Defect
- Attenuated Familial Adenomatous Polyposis
- Atypical Hemolytic Uremic Syndrome
- Auditory Neuropathy
- Auditory Perceptual Disorder
- Autoimmune Enteropathy
- Autoimmune Hemolytic Anemia
- Autoimmune Hepatitis
- Autoimmune Inner Ear Disease
- Autoimmune Lymphoproliferative Syndrome
- Autoimmune Pancreatitis
- Autosomal Dominant Partial Epilepsy With Auditory Features
- Autosomal Recessive Hyper IgE Syndrome
- Autosomal Recessive Polycystic Kidney Disease