TORONTO - Most teens are responsible when it comes to sexuality, but lack of knowledge about sexually transmitted infections and their consequences is a concern, says a new study.

The research, published in the January issue of Pediatrics and Child Health, found that 27 per cent of teens were sexually active at a mean age of 15 years.

The last time that they had sex, 76 per cent had used a condom, according to the findings.

"They don't know about many of the STIs that are common and they don't know about the consequences of the STIs,'' author Dr. Jean-Yves Frappier, head of the Adolescent Medicine Division at Sainte-Justine University Health Centre, said Monday in an interview from Montreal.

Five per cent of the sexually active teens said they had been diagnosed with an STI.

The teens surveyed overestimated the prevalence of HIV compared to other sexually transmitted infections, Frappier said.

"They don't know about chlamydia, which is much much more common,'' he said.

"Very few teens will be HIV positive but a certain percentage will be chlamydia positive in their teens. And that, they don't mention it.''

Sixty-nine per cent of teens surveyed could not find information they were looking for about sex, and 62 per cent reported obstacles in getting information.

Online interviews were conducted in October 2005 by Ipsos Reid with 1,171 Canadian teenagers aged 14 to 17. As well, 1,139 mothers of teenagers were interviewed, but these weren't the mothers of the teens who were surveyed. The results are considered accurate to within 2.9 percentage points, 19 times out of 20.

Frappier said parents have a responsibility to make information on sex and sexually transmitted infections available to their teens.

But that doesn't mean they have to deliver a lecture on STIs 101 at the breakfast table, he said.

Rather, they should give brochures, point out interesting websites and newspaper articles that provide information, and make an effort to find out how much their child has learned at school.

And quite often, he noted, information from parents about sex has to be repeated if the child isn't ready to hear it. The kids don't necessarily want to know about technical issues, but rather have questions about dating, violence in relationships, how to say `no' and how to know when they're ready.

"Teens are not at the same level at the same time,'' Frappier said.

"A 13-year-old can be ready to hear the information and another one can be miles away from that. He's not interested.''

The study found that at age 17, 45 per cent of those surveyed were sexually active, Frappier said.

Among those who were not sexually active, 71 per cent of the girls said they weren't ready, compared to 54 per cent of the boys.

About half of those who weren't sexually active -- both boys and girls -- said they hadn't found the right person.

Twenty-nine per cent of the girls said they wanted to wait until marriage, compared to 13 per cent of the boys.

In terms of role models, 75 per cent of the mothers surveyed believed that their teenagers' friends were significant role models when it came to sexuality, and 50 per cent mentioned entertainment celebrities.

But in fact, 45 per cent of teens regarded their parents as their role models, ahead of friends (32 per cent) and celebrities (15 per cent).

In addition, the study found 86 per cent of girls said they were attracted to boys only, while 87 per cent of boys said they were attracted to girls only.

Frappier said it's normal at that age for a certain percentage to have questions about their sexual orientation. He noted the minority responses would include those of teens identifying themselves as gay, as well as those who might have had a one-time attraction to someone of the same sex.

"It's more discussed so teens are more willing to admit on paper or on computer that it's their situation,'' he said.