John Mattson reports in Scientific American [with emphasis added here by us]:
Brahe died at age 54 after, as the story goes, he stayed at the table too long without relieving himself during a formal dinner, possibly bursting his bladder in the process.
That last legend may soon be challenged, as Brahe is being disinterred starting November 15 for analysis for the second time since he was buried in Prague in 1601. Testing on hair samples taken from Brahe’s tomb the first time, in 1901, showed an abnormally high mercury content in the astronomer’s body, raising the possibility that he had been poisoned. But Brahe may well have met his fate by less malicious means; for centuries medical practitioners applied mercury as a treatment for maladies such as syphilis.
(Thanks to investigator Celia Lu for bringing this to our attention.)