Sleep researchers have identified a condition which causes people to commit violent sexual acts in their sleep.

They called the condition "sleep sex" and were able to treat it with medication, in much the same way as sleepwalking is treated.

The patients experience disruptive sexual behaviour in their sleep, ranging from moaning to violent sexual advances.

"What was surprising was the duration of the abnormal behaviour and the fact that people weren't reporting it," Stanford Medical School psychiatrist Christian Guilleminault said in a statement.

In their study, appearing in the March/April issue of Psychosomatic Medicine, the Stanford researchers divided the eleven patients into three groups according to the severity of their symptoms.

In the first group were two women who made sexual sounds in their sleep. While embarrassing, their symptoms were considered relatively harmless.

The second group, consisting of a man and a woman, experience periods of violent masturbation in their sleep, which left them bruised and sore.

The third group was made up of six men and one woman who made unwanted, and sometimes violent, sexual advances on their partners.

In one case, a patient tried to strangle his wife.

Researchers at the Stanford Sleep Clinic found that the behaviours coincided with unusual brain-wave patterns and short interruption in sleep, just as sleepwalking does.

Standard sleep disorder treatments, including Valium-like drugs, worked in all but one of the cases.

Guilleminault said each of the patients had emotional problems which may have changed sleepwalking into sleep sex.

"What your state of mind is will colour the presentation" of the sleep disturbance, he said.