Purpose: To describe a magnetic resonance imaging (MRI) sign of pituitary apoplexy. Methods: The cranial MRI scans of 3 patients with pituitary apoplexy were retrospectively reviewed. Results: All 3 patients displayed a distinctive MRI sign of an enlarged pituitary gland with peripheral gadolinium enhancement surrounding a hypointense gland. Conclusions: The "pituitary ring sign" can aid in the early diagnosis and treatment of pituitary apoplexy. Copyright © Informa Healthcare.