The number of Canadian teenagers who say they've had sexual intercourse at least once is on the decline, Statistics Canada reported Wednesday.

In 2005, 43 per cent of teens aged 15 to 19 reported that they had sexual intercourse at least once, down from 47 per cent in 1996-1997.

The decline occurred due to young women. For them, the proportion who reported having had intercourse decreased from 51 per cent in 1996 to 43 per cent in 2005. Among young men, the proportion stayed unchanged at 43 per cent.

"As well, the proportion who reported becoming sexually active at a very early age decreased," wrote Michelle Rotermann of Statistics Canada's health information and research division in Ottawa.

"However, among those who were sexually active, there was no significant change in the likelihood of having multiple partners or, for males, using condoms. So while some adolescents have adopted measures to reduce their risks of sexually transmitted infection and unwanted pregnancy, others report high-risk behaviour."

Throughout the study period, the percentage of teens reporting intercourse was higher at older ages. About two-thirds of those aged 18 or 19 had had intercourse, compared with about one-third of those aged 15 to 17.

Condom use fades with age

Between 2003 and 2005, the proportion of sexually active teenage girls who reported using a condom rose from 65 per cent to 70 per cent. Among teenage boys, the proportion stayed around 80 per cent.

In 2005, 81 per cent of those aged 15 to 17 reported they had used a condom the last time they had intercourse, compared with 70 per cent among those aged 18 and 19, the report said.

Sex education seems to be paying off among younger teens in terms of greater condom use, said Alex McKay of the Sex Information and Education Council in Toronto.

But as teens get older or enter their 20s, they may become involved in long-term relationships. They may think the risk is lower because of the sense of permanency, go on the birth control pill and stop using condoms, McKay said.

Teens end up having unprotected sex with multiple partners before they reach their 30s, he said in an interview with CBC Newsworld on Wednesday.

The decline in condom use as teens get older points to the need to improve sex education to fight ignorance, particularly around sexually transmitted infections, McKay said.

The proportion of teens who reported becoming sexually active at an early age also declined. In 2005, eight per cent said had become active before age 15, down from 12 per cent in 1996-1997.

About one-third of teens aged 15 to 19 who had intercourse in the year before the survey reported having more than one partner, about the same percentage as in the earlier survey.

"It could be that girls are either lying, or they realize the harm and negative effects that sex can have on their life, on their relationship with their parents, with their friends," said Sara Harris, a 15-year-old shopping for back-to-school fashions in Toronto.

The report is based on interviews with about 4,500 teens in 1996, and about 10,000 teenagers for 2003 and 2005.