Thomas Aquinas addresses various economic activities in a manner scattered throughout his works, with each activity presenting distinct risks for different agents. Analysing his texts individually allows for the construction of a risk map addressing interest-based lending, commercial exchange and, at the boundaries of the market, the determination of the just exchange ratio (price or stipend) based on the nature of the good exchanged. This approach enables the reconstruction of what might be considered a Thomasian analysis of economic risk. The list of risks revealed by this mapping shows that risk affects all operations and agents in multiple ways. In his analysis, centred on an objective approach to the exchanged object and the nature of the operation, Aquinas highlights qualitative aspects of risk that are strikingly contemporary. However, the emergence of probability calculation in the modern era has often led to their neglect.