The mentally ill are frequently victims of violent crime
The mentally ill also have higher death rates from suicide and accidental causes.
The researchers, including the government's National Director for Mental Health in England, Professor Louis Appleby, said public and media attention usually focuses on the mentally ill as dangerous and as perpetrators of homicides.
Writing in the Lancet, they say more attention should be paid to the risk mentally ill people face of becoming murder victims themselves.
Death risks
The researchers from the University of Manchester and Aarhus, Denmark, looked at information from the Danish Psychiatric Case Register, and the Danish National Register for Causes of Death for 72,208 people.
All were on the psychiatric register, which records details of people admitted to hospital between 1973 and 1993.
Twenty-five per cent of deaths were from unnatural causes.
Of those 1% were homicides, 26% were accidental deaths and 73% were suicides.
It was found mentally ill patients were six times more likely to be murdered than people without mental illness.
Men with schizophrenia and people with affective psychosis (severe depression with delusions and hallucinations) have an even higher risk of being murdered.
The highest risks of death by both murder and accident were in patients with alcoholism and in patients who were drug users.
Drug users also had the highest risks of suicide.
Risk factors
In the Lancet paper, the researchers said although high risk of murder and those using drugs and alcohol might have been predicted, the reason for the high risk for male schizophrenics and those with affective psychosis was less clear.
They speculate their risk could be increased by factors including living in places with high murder rates such as inner cities, others are hostile to them because of symptoms such as irritability or paranoia, or they may be killed by other mentally ill people they come into contact with.
Professor Appleby told BBC News Online: "The first thing is to get the information out, because these are the sort of things clinicians need to think about."
"The other message is that this is the kind of information anti-stigma groups need, and allows us to tackle the issue head on."
He said reducing alcohol and drug misuse amongst the mentally ill was crucial because it would reduce their risk of being the victim of a homicide.
'Easy prey'
Marjorie Wallace, chef executive of the mental health charity Sane, said: "We have long been aware of the hidden fatalities among those suffering from mental illness and the greater risks arising through their own physical neglect.
"Much emphasis has been placed on the very rare headline cases where a mentally ill person has killed a stranger, while the real danger is to mentally ill people themselves.
"They are placed in tower blocks, hard to let flats and hostels in poorer areas, where they are easy prey to drug addicts and petty criminals.
"In our enthusiasm for every mentally ill person, however vulnerable, to live in the community, we have overlooked the need to protect them and their families as well as to educate the public."