Multi-source feedback tools, also known as 360 degree feedback, is a popular performance management and career development tool. Self-ratings of job performance are particularly useful in the performance evaluation process as it provides unique sources of information and helps employees to reflect on their own performance. Most research into discrepancies between self-observer multi-source feedback ratings has focused on the biases and validity of self-ratings. However, the extent to which an individual’s dysfunctional leadership tendencies are related to the discrepancy between self- and observer– ratings on their job performance remains unanswered. A total of 111 managers from various organisations completed a work-based personality questionnaire and their derailment traits were examined in conjunction with competency ratings collated from a multi-source feedback questionnaire (line manager, direct report, peer and self-ratings). Results revealed that dysfunctional leadership tendencies were positively related to a range of multi-source competency rating discrepancies. Exhibitionism and Over-confidence derailment traits in particular, were found to be strongly related to a number of self-observer competency rating discrepancies. Thus, managers’ inclination to over-inflate their own job performance in multi-source feedback might be an indication of their dysfunctional leadership tendencies. Implications of the study and directions for future research are discussed.