OBJECTIVES: Advances in understanding the neural underpinnings of intellectual disabilities (ID) such as fragile X syndrome (FXS) have led to clinical trials testing medications addressing disease-specific targets.  Individuals with ID ought to have a voice in consenting for clinical trials, but the extent to which they are capable of doing so is unknown. We discuss the importance of involving individuals with ID in the consent process and report results from a study of parents’ perceptions of their child’s ability to consent. METHODS: A survey was conducted with 422 families who had a child with FXS.  Parents rated items assessing their child’s ability to understand and complete six consent tasks.  They also provided information about themselves (maternal education, willingness to enroll child in a clinical trial) and their child (age, autism status, thinking/reasoning ability, gender). RESULTS: Factor analysis confirmed that the six items comprise a single factor.  However, we found a clear hierarchy of difficulty; the least difficult tasks were “understands that this medication is different from his/her regular treatment” and “realizes that he/she can choose to participate in the study or withdraw at any time.” The most difficult were “can make a decision about study participation” and “understands and weighs potential benefits and risks of participating in the study.” Although 29% of parents reported that their son was not at all capable of participating, the remainder exhibited a range of decisional skills. Factors associated with this variability include gender, autism, cognitive ability, age, and parents’ willingness to enroll their child in clinical trials. CONCLUSIONS: Parents rate many individuals with FXS as able to participate in the consent process, but they will likely need support to maximize effective participation.  We conclude with a brief review of strategies to support more inclusive participation in the consent process for people with ID.