Research addressing the microfoundations of knowledge sharing is emergent and growing, but there is still a lack of studies analyzing the trait of narcissism. This lack of studies appears relevant for middle-management figures, who increasingly play a strategic role in transferring knowledge, especially within professional organizations. This paper aims to study how three dimensions of narcissism, namely leadership/authority, grandiose exhibitionism, and entitlement/exploitativeness, impact the knowledge-sharing behavior of middle managers within organizations. A community of 115 Italian doctors who held middle management positions (head of ward unit) was investigated. The results indicate that leadership/authority and grandiose exhibitionism are negatively related to the propensity to share knowledge. In contrast, entitlement/exploitativeness has a positive relationship with the knowledge-sharing propensity. The study offers necessary evidence both for scholars and organizations.