Background: The best treatment option for patients with Graves' disease (GD) depends on each person's situation and how the differences between the treatment options matter to them in bringing resolution to their illness. The objective of this study was to develop and test an encounter decision tool (GD Choice) for patients and clinicians to engage in shared decision making about the treatment of GD. Methods: GD Choice was developed using an iterative process based on the principles of interaction design and participatory action research. To evaluate the impact of the tool, a controlled before–after study was conducted, assessing the use of GD Choice versus usual care (UC). Results: Sixty-eight patients were enrolled, 37 to UC and 31 to GD Choice. At baseline, the groups were similar. Treatment discussion length was similar in both arms. After their visit, patients in both groups had similar knowledge about the options, except for GD Choice patients knowing significantly more about the complications of tr...