Foster children went missing from care in England more than 17,000 times in a year according to new figures.
Ofsted revealed 5,060 children were reported as having gone missing while living with foster carers in 2014-15, compared with 4,245 the year before.
But the total number of instances of children going missing rose from 13,300 to 17,175.
Ofsted said the numbers were "an issue of concern" but believed better recording may in part explain the rise.
The South East and London reported the highest percentages of children going missing, 6% and 5% respectively, which "may be linked to the disappearance of children thought to be trafficked into the UK and removed from foster care".
Kent County Council, one of the largest local authorities, reported the biggest number of instances of missing children, 792, in 2014-15.
In England 155 children went missing from foster care for more than 28 days over the year, while 545 were missing for at least a week.
A further 1,845 were missing from one to six days and 2,515 were missing for less than 24 hours.
Ofsted's statistics also revealed more children going into foster care. There were 85,890 children and young people fostered in 2014-15, a 2% rise on the year before.
National director for social care at Ofsted Eleanor Schooling said: "The slight rise in children being placed in foster care again shows that it continues to be a valued choice of care for vulnerable young people, but also the ongoing need to recruit and retain more foster carers to meet increasing demand.
"We know that many children go on to have vastly improved outcomes from the care and support they receive.
"We continue to see an increase in the number and frequency of children in foster care who go missing. While the rise may be a result of better recording and awareness from services, this remains an issue of concern given the grave risks associated with children who go missing."
Councillor Roy Perry, Chairman of the Local Government Association's Children and Young People Board, said: "Councils work hard to ensure children are settled with foster carers, and any child missing from care for any length of time is a concern for everyone.
"While the increased numbers of children going missing is worrying, it is also a sign that identification and reporting of these incidents is continuing to improve, reflecting the heightened awareness of the dangers that this behaviour can pose.
"It is vital that councils and others continue to focus strongly on preventing children from going missing in the first place and providing effective help and support on their return home."