A psychological disorder was a condition which affected a patient's mental health.
In 2373, a claustrophobic Garak gave himself a pep talk while in a confined space, attempting to remind himself that "a disciplined mind does not allow itself to be sidetracked by niggling psychological disorders like claustrophobia". (DS9: "By Inferno's Light")
In 2374, Alzen tried to defend her covert studies of the crew of USS Voyager, explaining to Captain Kathryn Janeway that the data the Srivani uncovered could help them cure millions suffering from physical and psychological disorders. (VOY: "Scientific Method")