The disclosure by Democratic presidential nominee Hillary Clinton that she is being treated for pneumonia has once again raised the question of what candidates should tell voters about their health. Meanwhile, Donald Trump has promised to discuss his “personal health regimen” on The Dr. Oz Show on Thursday and to release the results of a recent physical. Both of the top candidates in 2016 have provoked repeated calls for them to release more complete medical records, a step that has in recent years become so expected during campaign season that its omission is noteworthy.

Looking at American history as a whole, however, the act of releasing any such records at all is rare.

As presidential historian Robert Dallek told NPR back in 2008, candidates and presidents have generally hidden their ailments from the public. And plenty of U.S. Presidents have served with health conditions that might have made voters think twice: Chester Arthur had a kidney problem; John F. Kennedy had chronic pain, among other health concerns; Woodrow Wilson, who was later laid low by a stroke, had already experienced at least one before his election.