The information listed below is provided for informational purposes only. There is no implied endorsement by POSSUM. POSSUM does not promote or endorse participation in any specific organization. Every effort is made to ensure that the details for each entry are as current as possible.
| Syndrome Name | POSSUM Number |
| Aarskog Syndrome Parents Support Group (USA) | 3001 |
| Aicardi Syndrome Foundation | 3018 |
| Alagille Syndrome Alliance | 3019 |
| Alport Syndrome Home Page | 4509 |
| Alstrom syndrome: International Alstroms Syndrome Newsletter | 3020 |
| American Cleft Palate-Craniofacial Association (ACPA) | |
| Androgen Insensitivity Syndrome (AIS) Support Group Australia | 4441 |
| Angelman Syndrome Foundation, Inc | 3462 |
| Alkaptonuria Society | 5998 |
| Ataxia-Telangiectasia Children's Project | 3033 |
| Bardert-Biedl, Laurence-Moon | 3276, 3113 |
| Batten Disease Support & Research Assn | 3333 |
| Beckwith-Wiedemann Support Network | 3036 |
| Birth Disorder Information Directory | |
| Blepharophimosis,Ptosis,Epicanthus Inversus Family Network | 3230 |
| CardioFacioCutaneous Syndrome Foundation | 3627 |
| CDG Syndrome | 5223 |
| Charcot-Marie-Tooth Association | 4384 |
| CHARGE Syndrome Fdn | 3480 |
| Chromosome 8 Home Page (Wells Labs) | 3416, 3184 |
| Chromosome 9p- Network | 3081 |
| Chromosome 11q: European Chromosome 11Q Network | 3087 |
| Chromosome 18 Support Groups | 3094, 3702, 3095,3096, 3699 |
| Chromosome 22 Central | 3132, 3186, 5359, 3703, 3267 |
| Coffin-Lowry Syndrome Foundation | 3150 |
| Coffin-Siris Syndrome Support Group | 3151 |
| Cornelia de Lange Syndrome Foundation | 3183 |
| Cri-du-Chat Syndrome Support Group | 3073 |
| Crouzon's Support Network | 3158 |
| DiGeorge Syndrome | 3132, 3186 |
| Down Syndrome WWW Page | 3100 |
| Dubowitz Syndrome Support | 3187 |
| Dwarfism/Short Stature | |
| Ehlers-Danlos National Foundation | 3212, 3128, 3406, 3203, 5410, 3392, 3264, 3482 |
| Ectodermal dysplasias: National Foundation for Ectodermal Dysplasia | 3208, 3209, 3524, 3137 |
| Fabry Disease Home Page | 3023 |
| Facio-Scapulo-Humeral Society, Inc | 5500 |
| FG Syndrome Family Alliance | 3566 |
| Fibrodysplasia Ossificans Progressiva: International Fibrodysplasia Ossificans Progressiva Association | 3223 |
| Foetal Alcohol Syndrome: National Organization on Fetal Alcohol Syndrome | 3218 |
| Foetal Alcohol Syndrome | 3218 |
| Fragile X: National Fragile X Foundation | 3324 |
| Fragile X: FRAXA Research Foundation, Inc | 3324 |
| Freeman-Sheldon Parent Support Group | 3156 |
| Galactosaemia: Parents of Galactosemic Children, Inc | 3789 |
| Gaucher: Gauchers Association | 4540 |
| Goldenhar Syndrome Research and Information Fund | 3339 |
| Incontinentia Pigmenti :National Incontinentia Pigmenti Foundation | 3265 |
| Jeune's Family Support Group | 3032 |
| Joubert Syndrome Foundation Corp | 3593 |
| Kabuki Syndrome Support | 3541 |
| Kabuki Syndrome: Supporting Aussie kids with Kabuki Syndrome | 3541 |
| Klippel-Feil syndrome: KFS Connection | 3274 |
| Klinefelter Syndrome Association, Inc | 3107 |
| Kniest Syndrome Support | 3272 |
| Langer-Giedion Syndrome Association | 3416 |
| Laurence Moon Bardet Biedl Syndrome Network | 3276,3113 |
| Lissencephaly Network, Inc | 3134, 5741 |
| Lowe Syndrome Association, Inc | 3340 |
| MAGIC Foundation for Children's Growth | |
| Mannosidosis: International Society for Mannosidosis & Related Disorders | 4458, 3745 |
| March of Dimes Birth Defects Foundation | |
| Marfan Syndrome: National Marfan Foundation | 3285 |
| Marinesco-Sjogren Syndrome Support Website | 3438 |
| Mitochondrial disorders: United Mitochondrial Disease Foundation | |
| Moebius Syndrome Foundation | 3217 |
| MPS: National MPS Society | 3308, 3309, 3310, 3311, 3312, 3313, 3314, 3315 |
| Myotublar Myopathy Resource Group | 5502 |
| Nager syndrome: Foundation for Nager and Miller Syndromes | 3143,3487 |
| Nail Patella Syndrome Support | 3331 |
| Neurofibromatosis: National Neurofibromatosis Foundation | 3332, 4258 |
| Neurofibromatosis: Neurofibromatosis Inc | 3332, 4258 |
| Niemann-Pick: National Niemann-Pick Disease Foundation, Inc | 3334 |
| Noonan Syndrome: Noonan Syndrome Support Group | 3335 |
| Norrie Disease Association | 3336 |
| Ollier & Maffucci Syndrome | 3121, 3759 |
| Opitz G/BBB Support | 3239, 3258 |
| Opitz Trigonocephaly Syndrome Family Network (OTSFN) | 3048 |
| Osler hemorrhagic telangiectasia syndrome | 3760 |
| Osteogenesis Imperfecta (OI) Foundation | 3349, 4350, 4351, 3366, 5691, 5692 |
| Phenylketonuria: National PKU News | 3533 |
| Pierre Robin Nework | 3371 |
| Prader-Willi: Prader-Willi Syndrome Association of Victoria | 3361 |
| Prader-Willi: International Prader Willi Syndrome Association | 3361 |
| Prader-Willi: Prader-Willi Syndrome Association | 3361 |
| The Proteus Syndrome Foundation | 3515 |
| Prune Belly Syndrome Network | 3003 |
| Pseudoxanthoma Elasticism International | 3345 |
| Rare Genetic Diseases in Children | |
| Rett syndrome: International Rett Syndrome Association | 3796 |
| Rett Syndrome Research Foundation | 3796 |
| Rett syndrome: Rett Syndrome Association UK | 3796 |
| Rubinstein-Taybi | 3384 |
| Russell-Silver: Association for Children with Russell-Silver Syndrome | 3385 |
| Septo-Optic-Dysplasia Support Group | 3398 |
| Shwachman-Diamond America | 3453 |
| Sotos Syndrome Support Association | 3055 |
| Spina Bifida Association of America | 3720 |
| Spina Bifida Resource Page | 3720 |
| Association for Spina Bifida and Hydrocephalus | 3720 |
| Spondyloepiphyseal Dysplasia (SED) and Spondylometaphyseal Dysplasia (SMD) | |
| Stickler Syndrome Support Group | 3030 |
| Sturge-Weber Foundation | 3397 |
| Sturge-Weber Foundation (Canada) Inc. | 3397 |
| Tay-Sachs: National Tay-Sachs and Allied Diseases Association | 3244 |
| Trisomy 18, 13 and related disorders: S.O.F.T | 3094, 3090 |
| Trisomy 9 Support | 3080 |
| Treacher-Collins Foundation | 3283 |
| Tuberous Sclerosis Alliance | 3417 |
| Turner's Syndrome Society of the United States | 3104 |
| Urea Cycle Disorders : National Urea Cycle Disorders Foundation | 3028, 4809 |
| VATER Association | 3425 |
| VATER Connection | 3425 |
| VCF Information Page | 3132 |
| Velo-Cardio-Facial Syndrome Educational Foundation | 3132 |
| Von Hippel-Lindau Syndrome : VHL Family Alliance and VHL Syndrome Homepage | 3676 |
| Williams Syndrome Association & Home Page | 3427 |
| Williams Syndrome Foundation Home Page | 3427 |
| WAGR/Aniridia Network | 3024 |