The purpose of this paper is to assess the relative importance of personality and organizational climate for two forms of heavy work investment; workaholism, a “bad” and work engagement, which represents a “good” kind of heavy work investment. An online survey was conducted among a sample of the Dutch workforce (N = 1,973) and the research model was tested using structural equation modeling. It appeared that, particularly neuroticism is related to workaholism, while all Big Five personality traits are related to work engagement (but predominantly openness to experience – positive; and neuroticism- negative). Moreover, workaholism is exclusively related to an overwork climate (and not to a growth climate), whereas work engagement is exclusively related to an employee growth climate (and not to an overwork climate). For the first time the simultaneous impact of personality and organizational climate on two different forms of heavy work investment is investigated. Since no interaction effects have been observed it means that of personality and organizational climate have an independent but also specific impact on both forms of heavy work investment (download the article).