Social relationships are a key component of quality of life, a high-priority outcome for autistic people, and family relationships are especially critical during adolescence. The PROMIS Family Relationships scale has been well validated for use with the general population, but psychometric validation in the autistic population has been lacking. This study investigated measurement invariance of the PROMIS Family Relationships scale among autistic and general population adolescents and found evidence of scalar invariance between the groups, indicating that the scale measures the same construct equivalently and that scores can be meaningfully compared. As the first study to examine measurement invariance of the pediatric self-report PROMIS Family Relationships scale in these populations, it demonstrates that the scale is valid for use with autistic teens. With an accurate tool to assess family relationships, this work highlights the importance of prioritizing and including autistic perspectives rather than relying solely on proxy reports.