The number of holidaymakers travelling abroad uninsured has risen in the last 12 months to 25%.
Research undertaken by ABTA earlier this month showed a jump from 22% when the same research was done last May.
Younger travellers are the most likely to travel abroad uninsured, and the numbers are rising.
Some 40% of those aged 18-24 and 38% of people aged 25-34 travelled abroad uninsured in the 12 months to May 2017.
Last year the number for both groups was 31%.
Of those who travelled abroad without insurance, 36% simply thought they did not need it while 22% stated that travelling uninsured was a risk they were willing to take.
"Every year we see cases of people falling into difficulty due to travelling without insurance," said Mark Tanzer, ABTA chief executive.
"Often their families have to raise thousands of pounds for their treatment or repatriation and that’s why it is so worrying to see an increase in younger people travelling without insurance. Rather than having to resort to the kindness of strangers, holidaymakers should make sure that they have the right insurance in place. I would urge all holidaymakers to make sure they take out an insurance policy this summer."
Susan Crown from the Travel Aware team at the Foreign and Commonwealth Office added: "We want people to enjoy their holidays but our research shows young people are risking thousands of pounds in medical bills by travelling without an insurance policy that covers them for everything they want to do abroad.
"The FCO cannot pay medical bills if you are hospitalised abroad nor can we fly you home."