This case report investigated the effects of hydrotherapy on an 11-year-old girl with Rett syndrome. The girl underwent hydrotherapy twice a week for 8 weeks using the Halliwick method. Her physical abilities were assessed before, during, and after the hydrotherapy sessions. The hydrotherapy reduced her stereotypical hand movements and improved her feeding skills, hand skills, walking balance, and interactions. The report concluded that hydrotherapy may decrease stereotypical movements and increase purposeful hand functions for individuals with Rett syndrome.