This study assessed diabetes mellitus risk in long-term Hodgkin lymphoma survivors, and found that a mean pancreatic tail dose of 36 Gy or higher was associated with a significantly increased risk of diabetes mellitus. This finding has important implications in the follow up of long-term Hodgkin lymphoma survivors, and also suggests that in newly diagnosed patients with upper abdominal involvement, the pancreas should be included as in organ-in-risk in the radiotherapy planning.