Business process models describe the way of working in an organization. Typically, business process models distinguish between the normal flow of work and exceptions to that normal flow. However, they often present an idealized view. This means that unexpected exceptions - exceptions that are not modelled in the business process model - can also occur in practice. This has an effect on the efficiency of the organization, because information systems are not developed to handle unexpected exceptions. This paper studies the relation between the occurrence of exceptions and operational performance. It does this by analyzing the execution logs of business processes from five organizations, classifying execution paths as normal or exceptional. Subsequently, it analyzes the differences between normal and exceptional paths. The results show that exceptions are related to worse operational performance in terms of a longer throughput time and that unexpected exceptions relate to a stronger increase in throughput time than expected exceptions.