In this paper we propose a systematic strategy for migrating crosscutting concerns in existing object-oriented systems to aspect-based solutions. The proposed strategy consists of four steps: mining, exploration, documentation and refactoring of crosscutting concerns. We discuss in detail a new approach to aspect refactoring that is fully integrated with our strategy, and apply the whole strategy to an object-oriented system, namely the JHotDraw framework. The result of this migration is made available as an open-source project, which is the largest aspect refactoring available to date. We report on our experiences with conducting this case study and reflect on the success and challenges of the migration process, as well as on the feasibility of automatic aspect refactoring.