Based on the stakeholder-agency theory, this study empirically investigates the impact of sustainability performance on financial performance. We rely on a sample from the German DAX30, MDAX, and TecDAX from 2008 to 2017. In contrast to former studies concentrating on the German market that tested a direct linear relationship between sustainability performance and financial performance, a time-lagging and curvilinear regression analysis was carried out, and evidence of a U-shaped relationship was found. This implies that sustainability management aiming at increasing financial performance should proactively strive for very high levels of corporate sustainability to meet the needs of investors and further stakeholders.