Researchers recorded cries from 39 6-month old infants, 21 of whom were at risk for autism because they had an older sibling with the condition.
The others were healthy babies with no family history of autism.
They said a computer-aided analysis showed the cries of babies at heightened risk for autism were higher and more variable in pitch than those of babies not at heightened risk for autism, 'MyHealthNewsDaily' reported.
The result was only true when the cries were caused by pain, such as when a baby fell and bumped his or her head, said study researcher Stephen Sheinkopf from Brown Alpert Medical School's Women and Infants Hospital.
By the time the children in the study were 3 years old, three of them were diagnosed as having autism. As babies, these three children had cries that were among the highest in pitch, the researchers said.
They also had cries that sounded more tense, with more "background noise" picked up by the computer analysis.
However, the differences in the autistic babies' cries could probably not be detected by most people using their ears alone, so this is not something parents should listen for, Sheinkopf said.
"We don't want parents to be anxiously listening to their babies' cries," he said.
The findings suggest babies' cries at 6 months might be used, along with other factors, to determine a baby's risk for autism early on, the researchers said.
According to Sheinkopf, this finding could allow researchers to identify children at risk for autism long before the typical behaviour problems become apparent.