Smoking portrayed in feature films dramatically increases the number of teenage smokers, suggests a new study published in the Lancet's June issue.

"Here's more evidence that movies have a strong impact on adolescents," said Madeline Dalton, the study's lead author.

"Previous studies suggested that smoking in movies influences adolescent smoking behaviour, but this is the first study to show that viewing smoking in movies predicts who will start smoking in the future."

In 1999, researchers from Dartmouth Medical School and the Norris Cotton Cancer Center surveyed children aged 10 to 14 on a variety of behaviours, including smoking and movie watching.

About 3,500 of the kids surveyed had not tried smoking.

One to two years later, the researchers surveyed 2,600 of the original group to determine if they had tried or started smoking.

They found that 10 per cent of the teens had tried smoking, and that there was a correlation between the amount of smoking seen in movies and first-time smokers.

Adolescents who had seen the smoking in movies were more than two and a half times more likely to start smoking compared to children who had seen the least amount of smoking, researchers wrote.

"Our data indicate that 52 per cent of smoking initiation among adolescents in this study can be attributed to movie smoking exposure," said Michael Beach, co-author of the study.

Beach said it suggests that reducing an adolescents' exposure to smoking in movies could reduce the number who start smoking.