Police say a 47-year-old man was beaten to the upper torso and head during the brawl inside the behavioral health services ward at Interfaith Medical Center.
He was found unresponsive by police officers responding to the eighth floor on the report of a fight just before 10 p.m. Tuesday.
The patient was pronounced dead at the hospital.
Another patient, a 20-year-old man, was taken into custody in the beating. Charges are expected.
The fight is believed to have broken out in the bathroom, where there are no surveillance cameras.
The behavioral health services ward has heavy security, but patients are not continually monitored while in the bathroom.
The two men were playing dominoes before the fight. The game was believed to be peaceful, and the reason for the dispute was not immediately known.
There were no other witnesses to the fight.
No weapon was recovered, and it is possible the fight was hand-to-hand combat.