Background: There is a need for promoting exercise practice among people with intellectual disabilities (ID). Aquatic exercise (AE) could be a viable option in this regard.Objective: To identify and critically analyze the best available evidence concerning the effects of AE in the physical and mental health of people with ID. Methods: A systematic review of randomized controlled trials (RCTs) and comparative studies was performed after searching within several databases up to March 2021. Results: A total of 4 RCTs and 3 comparative studies were found. Their methodological quality ranged from high to low. Aquatic interventions had positive effects on cardiorespiratory, muscular fitness and balance. Mixed effects were seen on parameters related to obesity and cognition. Scant information regarding feasibility and intervention fidelity was provided. In general, interventions details were not discussed in deep. Conclusion: Preliminary evidence shows that aquatic exercise can be prescribed to people with ID in order to improve their physical health. The impact of aquatic exercise on motor skills, cognitive function and mental health remains unclear. Further research on this topic should provide a detailed description of the interventions carried out, including information on the feasibility and intervention fidelity.