Chronic graft-versus-host disease (GVHD) is the prime cause of transplantation-related mortality late after marrow grafting and contributes directly or indirectly to most nonmalignant complications. The main clinical symptoms and diagnostic problems of chronic GVHD are summarized here. A major issue in treating chronic GVHD is to assess disease severity. A critical review of published grading systems failed to demonstrate that any system is better than the others. Prospective validation of the Johns Hopkins grading scale is timely and warranted.