Building on critical literature on corporate sustainability, we add a perspective thus far only scarcely addressed: The toxicity of financial products imposing systemic risk. We start with various illustrative cases from the financial sector which have also been discussed colorfully in the media. This sets the stage for toxic assets and practices as revealed after the onset of the financial crisis precipitated by the collapse of Lehman Brothers. To illustrate corporate toxicity we use the “Global 100 Index” from “Corporate Knights” to show which (financial) scandals or bailouts cases were detected at corporations awarded a position in the prestigious sustainability rating. Subsequently we develop the concept of ‘toxicity’ adopted from pharmacology as a meta-criterion, which, as we argue, should be added to the concept of Corporate Social Responsibility (CSR) and the ESG (environment, society, governance) universe. We discuss implications for theory development and the overall credibility of corporate sustainability ratings.