Self-determination is a characteristic that encompasses an individual’s abilities and attitudes to act as one’s own agent (Wehmeyer, 1992). Individuals with increased self-determination may act according to their beliefs and preferences more than individuals who are less self-determined, which in turn may lead to increased decision-making opportunities. Encouraging self-determination is a key strategy to reduce disparities faced by individuals with intellectual and developmental disabilities (I/DD; Shogren, Wehmeyer, Reese, & O’Hara, 2006). Although fragile X syndrome (FXS) is the most common known genetic cause of intellectual disability and autism spectrum disorder, no studies have examined factors associated with self-determination in this population.