Teenage smoking in England has fallen after introduction of a law that forbid buying cigarettes before 18 years of age.
Smoking rates among young people aged 16 and 17 fell from 24 percent to 17 percent after the law changed in October 2007, a Cancer Research study found.
The findings, published in the journal Addiction, are based on a survey of more than 1,100 young people in that age group across England.
Cancer Research said the results were evidence that tobacco policies could make a difference.
Jenny Fidler, the report's lead author who is based at Cancer Research UK?s health behaviour research centre at University College London, said: ?The new law looks to have helped reduce smoking prevalence among younger age groups.
"This is good news for the future health of this generation of young people and shows that tobacco policies can make a real difference.?
Before 2007 retailers could legally sell cigarettes to anyone over the age of 16 in England, Scotland or Wales, while the same was true in Northern Ireland until 2008.
According to Cancer Research figures, more than 80 percent of smokers start the habit before the age of 19, and half of all long-term smokers will die of cancer or other smoking-related diseases.
The charity says stopping young people from starting smoking is essential in order to reduce the death toll.
Jean King, Cancer Research UK?s director of tobacco control, said: ?This result is encouraging. We would like to have seen an even bigger drop in the number of young smokers but any measure that helps stops young people from smoking is a step in the right direction.
?We need to do more to protect young people. We urge the government to prevent more lives being lost to an addiction that will kill half of all long term smokers."
She said regulations banning tobacco displays in shops and cigarette vending machines were "needed and wanted by the public".
A Department of Health spokesman said discussions were being had on how to further tackle smoking.
He added: "We welcome these findings as nearly all adults who smoke get hooked when they are young.
"Smoking is the biggest preventable cause of death in England, causing over 80,000 premature deaths in England each year."