Organizations increasingly encourage, recognize, and reward ethical leadership to preempt the economic and reputational risks associated with ethical failures. At the same time, organizational leadership positions are disproportionately occupied by individuals higher in narcissism. This paper highlights how the combination of these two phenomena carries important organizational implications by examining how ethical leadership behaviors differentially impact leaders based on their level of narcissism. Building upon self-concordance theory, we introduce a model of contingent consequences of ethical leadership. Our model identifies motivational (i.e., self-efficacy of the leader) and social (i.e., admiration of the leader) mechanisms that explain why ethical leadership positively predicts leadership effectiveness for some leaders but not for others. We test our model using a field study and two experiments. Findings from these three studies point to a problematic leadership paradox: when leaders higher in narcissism behave more ethically, they incur higher motivational costs and reap fewer social benefits compared to their peers who are lower in narcissism. Results reveal risks to leadership effectiveness for narcissistic leaders who attempt to lead more ethically. We discuss implications for ethical leadership research and practice.