Background: The study aimed to identify the perceived role and significance of typically developing siblings in the emergence of self-determination in their brothers/sisters with intellectual disabilities. Method: The study material consisted of information from individuals with intellectual disabilities. The analytical method relied on grounded theory methodology procedures. Results: Three main themes were identified in what young adults with mild intellectual disabilities shared about their typically developing siblings: attitude toward self-determination, the degree of involvement in and influence on the self-determination process and the level of (mis)alignment with the parental approach in this regard. Conclusions: The results of this study show how young adults with intellectual disabilities perceive the role of their siblings in their pursuit of self-determination. The individuals with intellectual disabilities were demonstrated to be empowered to express their views, provided they had the right conditions and were given adequate opportunities.