The goal of this paper is to describe the link between financial performance and the level of sustainability. In a novel approach, the paper classifies firms based on past financial success to address a potentially reciprocal relationship. For the groups of better and worse performing firms and for the entire sample, the above link is then tested, also accounting for non-linearity in the relationship. We show that environmental management system (EMS) implementation as a proxy for a firm's sustainability level is only positively associated with the financial performance of financially well-performing firms. Conversely, it has a negative association with the performance of less good firms. We show that this implies that firms cannot change from good to bad performance, and vice versa, solely through the implementation of an EMS, and also that the result remains when introducing non-linearity in the link. Based on this result, we discuss implications for the direction of causality.