To evaluate the effects of aquatic exercise therapy on gait variability and disability compared with usual care for people with Parkinson disease (PD).Single-blind randomized controlled trial.Community-based hydrotherapy pool.Individuals with PD (Hoehn-Yahr stages I-III) (N=21).Participants were randomly assigned to either an aquatic exercise therapy group (45min, twice a week for 6wk) or a group that received usual care.The primary outcome measure was gait variability as measured using a motion capture system. Secondary outcomes were quality of life measured on the Parkinson's Disease Questionnaire-39 and freezing of gait and motor disability quantified by the Unified Parkinson's Disease Rating Scale. Feasibility was evaluated by measuring safety, adverse events, and participant satisfaction.People in the aquatic therapy group and usual care group showed similar small improvements in gait variability. The aquatic therapy group showed greater improvements in disability than the usual care group (P<.01). No differences between groups or over time were identified for freezing of gait or quality of life. Aquatic therapy sessions were safe and enjoyable with no adverse events.Aquatic therapy appears feasible and safe for some people in the early stages of PD.