Candidates’ assertive impression-management (IM) behaviors affect performance ratings during selection interviews, a finding that has caused some concern about selection interviews’ objectivity and accuracy. Similar effects have been proposed for assessment centers, yet research on IM in assessments centers is rare and inconclusive. This study uses trait-activation theory (Tett & Guterman, 2000) to predict how assertive IM-behaviors emerge and influence performance ratings during assessments centers. Results showed that candidates’ ingratiation behaviors related to observer ratings on the conceptually related AC-dimension cooperation, whereas self-promotion behaviors related to ratings on the dimensions leadership and planning. Furthermore, assertive IM behaviors during the assessment center construct-related validity and correlated significantly with candidates’ performance in non-evaluative situations. Consequently, assertive IM behaviors in personnel selection may pose less of a threat than frequently assumed but may partially reflect a behavioral manifestation of candidates’ underlying interindividual differences.