The increasing attention towards the environmental impact of IT (information technology) demands reorientation from IT departments. Research has outlined that the importance of Green IT is related to IT business alignment and environmental initiatives while uncertainty potentially derives from missing standards, measurements, or missing internal support for Green IT. We assume that importance and uncertainty are main determinants for Green IT adoption. These theoretical assumptions still lack empirical validation. As a contribution to the ongoing discussion of Green IT, we analyze data from 116 IT departments on the predictors of Green IT adoption using multinomial logistic regression. It is shown that the outlined assumptions prove to be statistical significant. These findings contribute to existing knowledge on Green IT and provide practical recommendations for CIOs, IT managers, environmental and sustainability managers as well as new opportunities for further research in this field.