Background: The behavioral and emotional functioning of typically-developing (TD) siblings of youth with autism spectrum disorder (ASD) has been frequently assessed in the literature; however, these assessments typically include only one informant, rarely considering differences between parent and self-reports of sibling adjustment. Aims: This study examined parent-youth reported informant discrepancies in behavioral and emotional functioning, including whether parent and youth reports yielded the same conclusions regarding TD sibling risk status. Methods, procedures, and results: Among 113 parents and TD siblings of youth with ASD, TD siblings self-reported more overall, conduct, hyperactivity, and peer problems (compared to parent reports). Although few siblings were considered at-risk, those who were identified were not usually identified as at-risk on both informants’ reports. Moreover, ASD symptoms, broader autism phenotype symptoms, parent mental health concerns, and social support from parents were all related to differences in at-risk classification between parent- and sibling self-report. Conclusions and implications: This paper highlights the necessity of multi-informant reporting when considering TD sibling psychological functioning. What this paper adds: This study helps to address gaps in the literature on assessment of emotional and behavioral functioning of TD siblings of youth with ASD. The results highlight the importance of utilizing both parent- and self-report when identifying TD siblings at-risk for maladjustment. Although few siblings were considered at-risk, those who were identified were not usually identified as such on both informants’ reports, and a variety of sibling- and parent-factors were associated with differences in at-risk classification. Thus, inclusion and examination of both parent- and self-report of TD sibling psychological functioning is vital for accurately identifying numbers of TD siblings at-risk of maladjustment.