https://doi.org/10.1177/1044389421992289 Families in Society: The Journal of Contemporary Social Services 2021, Vol. 102(4) 548–555 © The Author(s) 2021 Article reuse guidelines: sagepub.com/journals-permissions DOI: 10.1177/1044389421992289 journals.sagepub.com/home/fis Research Note The sibling relationship has been accepted as one of the most significant family subsystems. Siblings are a crucial source of familial support during the lifespan by serving as friends and confidants in early years (McHale et al., 2012) and emotional supporters for each other during parental conflict and at different life stages (Waite et al., 2011). Siblings who have positive relationships with one another in adulthood are less likely to feel lonely and highly likely to report greater life satisfaction (Milevsky, 2005). Research in the 1980s, focused mostly on sibling relationships in the early years of life (e.g., C. Stocker et al., 1989). Research on adult sibling relationships became of interest after Cicirelli’s (1995) seminal paper high- lighted the significant changes in sibling rela- tionships across the life span, and particularly during emerging adulthood. These adult changes included individual roles in life reori- entation, marriage, parenthood, additional edu- cation, and occupation that influenced family and sibling dynamics (Conger & Little, 2010). 992289FIS XX X 10.1177/1044389421992289Families in SocietyGungordu et al. research-article 2021 1 MA, MS, graduate research assistant, University of Alabama, Tuscaloosa, USA 2 PhD, professor & director of Pediatric Development Research Lab, University of Alabama, Tuscaloosa, USA 3 PhD, assistant professor, Ewha Womans University, Seoul, Republic of Korea 4 PhD, associate professor & director of Center for the Study of Ethical Development, University of Alabama, Tuscaloosa, USA Corresponding Author: Ms. Nahide Gungordu, University of Alabama, 1619 Capital Hall, Tuscaloosa, AL 35487-0166, USA. Email: ntosyalioglu@crimson.ua.edu The Reliability and Validity of the Lifespan Sibling Relationship Scale (LSRS) With an English-Speaking Young Adult Sample Nahide Gungordu 1 , Maria Hernandez-Reif 2 , Youn-Jeng Choi 3 , and David-Ian Walker 4 Abstract The Lifespan Sibling Relationship Scale (LSRS) is the most comprehensive self-report questionnaire available to evaluate the quality of sibling relationships based on feelings, behaviors, and opinions across child and adult periods of development. To the best of our knowledge, the psychometric properties of the LSRS have not been assessed or reported in an English-speaking population since this assessment tool was introduced 20 years ago. The current study examined the internal reliability and construct validity of the LSRS with a sample of 370 young adults living in the United States. Results indicated that the original six-factor model of the LSRS is plausible with minor modifications to measure the sibling relationship quality and with its close correlation between factors and scales. Keywords lifespan sibling relationship scale, psychometrics, reliability, siblings, validity, young adults Manuscript received: November 3, 2020; Revised: December 2, 2020; Accepted: January 5, 2021 Disposition editor: David C. Kondrat