With the advent of UML and MDA, models play an increasingly important role in software development. Hence, the management of the quality of models is of key importance for completing projects succesfully. However, existing approaches towards software quality focus on the implementation and execution of systems. These existing quality models cannot be straightforwardly mapped to the domain of UML models as source code and models differ in several essential ways (level of abstraction, precision, completeness and consistency). In this paper we present a quality model for managing UML-based software development. This model enables identifying the need for actions for quality improvement already in early stages of the life-cycle. Early actions for quality improvement are less resource intensive and, hence, less cost intensive than later actions. We discuss our experiences in applying the quality model to several industrial case studies. Finally we present a tool that visualizes our quality model. This tool helps in relating management level quality data to detailed data about specific quality subcharacteristics.