Nowadays, nothing is more critical for business than dealing with environmental degradation. Drawing upon the Upper Echelon Theory, this study delves into the nuanced influence of CEO narcissism on corporate environmental performance. Unlike previous research that treats narcissism as a single construct, this work distinguishes between its two primary dimensions: grandiose and vulnerable narcissism. Based on a sample of 214 observations of Spanish firms over the period 2015-2020, the research findings reveal a divergent impact. On the one hand, the results show stronger corporate environmental performance when CEOs predominantly exhibit traits of grandiose narcissism, likely driven by a desire for visibility and social recognition. On the other hand, corporate environmental performance is significantly weaker when CEOs manifest traits of vulnerable narcissism, characterised by low extroversion. In addition, we analysed the moderating role of CEO duality in the above relationships. The results indicate that when the CEO also chairs the board of directors, the negative effects of vulnerable narcissism on environmental performance of firms are more pronounced. These findings provide valuable insights for boards of directors regarding the selection of a new CEO, the design of governance mechanisms and the strategic importance of CEOs psychological traits aimed at ensuring corporate environmental sustainability.