Although it is not yet known whether the man who attacked and killed an Upper East Side psychologist in her office on Tuesday night was a patient or otherwise connected to her practice, the murder raises a difficult question that hovers over the fields of psychology and psychiatry: In deciding to treat mentally disturbed patients, do therapists put themselves at risk?

A forensic psychiatrist at Saint Vincent’s Hospital and New York Medical College, Spencer Eth, said that, as far as he knew, there were no statistics about how often therapists are killed by patients. Injuries are more common, he said, and both emergency rooms and inpatient psychiatric units rank relatively high on lists of dangerous workplaces.

There have been notable cases of murders. In 2006, a researcher at the National Institute of Mental Health and a prominent expert on schizophrenia, Wayne Fenton, was beaten to death by a 19-year-old patient whom he saw in a private office on a Sunday afternoon. Just last week, a therapist in North Andover, Mass., who treated children with chronic mental illnesses, was stabbed to death by a teenage client to whom she paid a house call.

The therapist who was killed in New York City, Kathryn Faughey, was a psychologist who, according to her Web site, used cognitive behavioral techniques to address problems like “relationship issues,” “anxiety, depression, panic attacks, coping with stress,” and “changing life conditions” such as “employment changes, relocations, or breakups.” Faughey’s is not the kind of practice that would normally have included patients who are at risk for violent behavior, making the identity and motive of her attacker more mysterious.

For psychiatrists who treat patients with schizophrenia, bipolar disorder, or severe depression with psychotic features, becoming the victim of an attack is a real possibility. They are trained to take precautions, particularly on an initial visit, when the doctor doesn’t know the person’s history and mental condition. Many psychiatrists who see such patients prefer to practice in group offices or in a hospital, Dr. Eth said.

If seeing patients in a private office, “you should have some kind of alarm system, a buzzer, a light, something that will trigger a call for help,” the president of the Treatment Advocacy Center in Arlington, Va., and the author of several books on mental illness, E. Fuller Torrey, said.

The most common cause of violence is a patient not taking medication and becoming psychotic and delusional, Dr. Torrey said. “Usually it’s part of the paranoid delusional system,” he said. “You’re not dealing with a rational motive. You’re dealing with, ‘My therapist is trying to steal my brain,’ or ‘He’s trying to poison me,’ or ‘He’s in cahoots with the CIA, and he’s been tapping my phone or spying through my television set.'”

Another potential cause, according to Dr. Eth, is “erotomania,” a condition in which a patient becomes romantically obsessed with a therapist and may falsely believe that the therapist returns his or her love. “There have been therapists who are followed by patients when they leave the office,” Dr. Eth said, “or who receive disturbing phone calls at home from patients or former patients.”

Sometimes a patient’s spouse may become enraged at a therapist who he or she feels is turning the patient against him, Dr. Eth said.

In other instances, an individual may be sent to a psychiatrist for an evaluation — to determine whether he or she can return to work, for example, or regain custody of a child — and may be dissatisfied with the result of the evaluation.

“Lots of those kinds of situations can feel threatening,” Dr. Eth said.