Hilary Dawn Cass is a British honorary physician in paediatric disability at the Evelina Hospital, part of Guy's and St Thomas' NHS Foundation Trust, and former president of the Royal College of Paediatrics and Child Health. She is known for establishing the UK's Rett Clinic for children with Rett syndrome in 1992, developing palliative care for children, and leading the Cass Review, completed in 2024.