Background. Polish studies have not been focused on the method enabling a reliable and valid measure of the psychological attributes of sibling relationships in the period of adulthood. Aim. The aim of this study was to determine the psychometric properties of the Polish adaptation of the Adult Sibling Relationship Questionnaire (ASRQ). methods. The study included 406 students of different majors of the University of Łódź and the Łódź University of Technology. In the surveyed group, 58.9% were women (n=239) and 41.1% men (n=167). The participants of the survey were adult, aged from 18 to 35 years (M=23.7,SD=3,891). Results. The three main ASRQ factors (Warmth, Conflict, Rivalry) showed good internal consistency (Cornbach's α .87-.97). Correlations between the individual scales creating the main factors demonstrate similar patterns to the results obtained by the authors of the original version of the ASRQ. The results of the conducted exploratory (EFA) and confirmatory (CFA) factor analyses confirm the factorial structure of the original version of the ASRQ. discussion. The presented results indicate that the ASRQ in the Polish adaptation is a reliable and valid multidimensional measure of relationships between siblings in early adulthood. Conclusions The Polish adaptation of the Adult Sibling Relationship Questionnaire can open an era of the researchers' interest in the subject area of relationships between siblings in the period of adulthood.