Researchers from the University of Waterloo in Canada surveyed children between the ages of six and 16, and all within a month of their diagnosis with asthma, food allergy, epilepsy, diabetes or juvenile arthritis.
According to parents' responses to a standardised interview, 58 per cent of children screened positive for at least one mental disorder.
"These findings show that risk for mental disorder is relatively the same among children with different physical conditions," said Mark Ferro, from the University of Waterloo.
Six months after diagnosis, the number of kids showing signs of a mental disorder dipped slightly to 42 per cent.
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According to the study published in the journal BMJ Open, anxiety disorders were most common, including separation anxiety, generalised anxiety and phobias.
"It is possible that the number is higher very early because there is some uncertainty surrounding the prognosis, or unanswered questions about management and treatment," said Alexandra Butler, from the University of Waterloo.
The researchers found that age and gender had no impact on the results. A subset of kids self-reported on their own mental health. Where 58 per cent of parents reported that their children presented signs of a mental health problem, only 18 per cent of kids reported it.
This result speaks to the need for health professionals to get multiple perspectives when assessing children's mental health.