A first-ever survey of parents shows, that nearly half say their child has wandered off at least once.
The more severe the autism, the more likely the child was to walk away.
Often the child went in search of something, not because they were confused or lost.
But more than 300 were gone long enough to cause concern, so experts say parents need to take precautions.
Thomas Frazier, Ph.D., a neuropsychologist, says, "Putting alarms on the major doors of the house so that if the child were to wake up in the middle of the night, or even in the middle of the day if the parent was distracted, or making dinner or lunch, the child opens the door and the door alarm goes off and the parent becomes aware that they're leaving the house."
It's hoped the survey will help parents - and first responders searching for missing kids - better understand the problem.