Achieving a bright digital future requires knowing and managing the adverse effects of digitalization. The objective of this paper is to identify, structure, and communicate the most severe adverse risks and side effects of digitalization. To this end, we apply an iterative taxonomy development process informed by academic literature, journalistic articles, and expert interviews. The result is a comprehensive multi-level taxonomy of the adverse effects of IT use. The taxonomy shall serve as platform for further research on identifying and managing the risks and side effects of digitalization. It supports information system scholars in proper net benefit assessments of the effect of increasing use of ever more intelligent, inter-connected, and pervasive IT-based systems. Further, it supports the anticipation and management of adverse effects in the design of such systems.