The purpose of this study was to test whether a multisource performance appraisal instrument exhibited measurement invariance across different groups of raters. Multiple-groups confirmatory factor analysis as well as item response theory (IRT) techniques were used to test for invariance of the rating instrument across self, peer, supervisor, and subordinate raters. The results of the confirmatory factor analysis indicated that the rating instrument was invariant across these rater groups. The IRT analysis yielded some evidence of differential item and test functioning, but it was limited to the effects of just 3 items and was trivial in magnitude. Taken together, the results suggest that the rating instrument could be regarded as invariant across the rater groups, thus supporting the practice of directly comparing their ratings. Implications for research and practice are discussed, as well as for understanding the meaning of between-source rating discrepancies.