Peacekeeping missions may affect soldiers' mental health, doctors have warned.
Much research has focussed on soldiers on active duty
Researchers writing in the British Medical Journal surveyed soldiers in Northern Ireland in the early 1990s and showed high levels of psychiatric illness.
They warned those now serving in Kosovo or Bosnia might also be affected.
But the Ministry of Defence said it had introduced measures over the last decade to improve soldiers' wellbeing.
Anxiety and isolation
Researchers from Guy's, King's and St Thomas's School of Medicine in London surveyed 150 soldiers from all ranks of an infantry battalion two weeks before they were deployed to Northern Ireland and again two weeks before the end of a six month tour between 1993 and 1994.
Their mental health was assessed using a recognised test which asked about anxiety, loneliness and social interaction.
It was found there were high levels of psychological illness, with soldiers three times more likely to suffer physical and psychological symptoms after their tour, with 32 more soldiers were affected after.
Symptoms of anxiety and social isolation increased significantly, but ratings for depression did not change.
The researchers say many studies have looked at how fighting wars can damage soldiers' mental health but the effect peacekeeping missions has not been examined. They say more work should be done.
Jane Ogden, a reader in health psychology who carried out the research, told BBC News Online: "Soldiers on these kind of missions do have an enormous amount of time when they are cooped up and not doing anything. But they may then have to go out and risk being exposed to dangerous situations."
Dr Geoff Lawrenson, a GP at Colchester Garrison in Essex who co-ordinated the anonymous survey when he was serving in Northern Ireland, added: "There are certain aspects of service life, such as cramped living conditions and the periods of inactivity followed by periods of stress, which contribute to psychological problems.
"The problems that affected soldiers in Northern Ireland are those that affect security operations in Bosnia or Kosovo."
He said initiatives to improve communication with families and the opportunity for "rest and relaxation" had been introduced in the last nine years.
"I hope these have prevented the majority of psychological problems. But we need more research on this, other than that which we carried out."
But a spokeswoman from the Ministry of Defence rejected the findings as out of date.
She said soldiers had up to 24 months between tours of duty, and support and links with home had been improved while they were away.
"It's unfair to compare how we look after soldiers in 2003 with a survey carried out almost 10 years ago.
"The welfare of our service personnel is an important factor for all commanders. We recognise that they are often placed in potentially dangerous locations, but we seek to ensure that they are provided with the best support possible and prepared for the mental challenges they might face."