Hearing voices may affect over a fifth of schoolchildren aged 11 to 13, a psychiatric study has found.

In most cases, the auditory hallucinations stop with time, the findings show. But children who continue to hear voices could be at risk of mental illness or behavioural disorders.

Researchers carried out psychiatric assessments of almost 2,500 children aged between 11 and 16 in Dublin.

They discovered that 21%-23% of younger adolescents, aged 11 to 13, had experienced auditory hallucinations.

Of this group, just over half were found to have a non-psychotic psychiatric disorder such as depression.

Just 7% of older adolescents aged 13 to 16 reported hearing voices - but almost 80% of those who did had a diagnosable psychological problem.

Lead researcher Dr Ian Kelleher, from the Department of Psychiatry at the Royal College of Surgeons, said: "We found that auditory hallucinations were common even in children as young as 11 years old."

"Auditory hallucinations can vary from hearing an isolated sentence now and then, to hearing 'conversations' between two or more people lasting for several minutes.

"It may present itself like screaming or shouting, and other times it could sound like whispers or murmurs. It varies greatly from child to child, and frequency can be once a month to once every day.

"For many children, these experiences appear to represent a 'blip' on the radar that does not turn out to signify any underlying or undiagnosed problem.

“However, for the other children, these symptoms turned out to be a warning sign of serious underlying psychiatric illness, including clinical depression and behavioural disorders, like attention deficit hyperactivity disorder.

"Some older children with auditory hallucinations had two or more disorders. This finding is important because if a child reports auditory hallucinations it should prompt their treating doctor to consider that the child may have more than one diagnosis."

The findings are published in the British Journal of Psychiatry.

Co-author Professor Mary Cannon, also from the RSCI's Department of Psychiatry, said: "Our study suggests that hearing voices seems to be more common in children than was previously thought.

“In most cases these experiences resolve with time. However in some children these experiences persist into older adolescence and this seems to be an indicator that they may have a complex mental health issue and require more in-depth assessment."