Three studies sought to translate the Relationship Disillusionment Scale (RDS-English Version) into Polish, evaluate the new scale’s psychometric properties, and extend previous validation work on the instrument. After translation and back-translation of the RDS-English Version, Study 1 administered the RDS-English Version to 20 bilingual university students in Poland, followed two months later by the Polish-language version RDS-PL. Cross-language test-retest reliability was .59. Study 2 administered the RDS-PL to 318 individuals in an online survey, who completed additional Polish-language measures to examine convergent and discriminant validity. Confirmatory factor analyses generally supported a one-factor solution for the RDS-PL. Significant correlations in the expected direction with variables such as relationship commitment, relationship depth, forgiveness-benevolence, and resentment-avoidance supported the convergent validity of the RDS-PL. Study 3, which surveyed 280 bilingual individuals online, documented invariance of RDS-PL factor loadings between ever-married and non-married participants. In addition, several Polish- and English-language variables (e.g., satisfaction, conflict intensity/reactivity, commitment, intimacy) correlated with the RDS-PL (more strongly in married than unmarried participants), further supporting the convergent validity of the RDS-PL. Studies 2 and 3 also provided modest support for its discriminant validity.