One in five Kiwis are not using condoms the first time they have sex, a survey has found.
While it was an improvement since the 1970s, when less than 40 per cent were using condoms in their first sexual encounters, health officials said the findings reinforced the need for greater condom use.
New Zealand's first comprehensive sexual health survey, conducted in 2015 with more than 10,000 New Zealanders aged 15 years and over, found 80 per cent of people between 16 and 24 years old used condoms in their first sexual encounters.
"Condom use is vitally important for both preventing unwanted pregnancies as well as sexually transmitted infections – particularly in light of recent increases in the number of people with syphilis," Ministry of Health deputy director of public health Dr Niki Stefanogiannis said.
There were 470 cases of syphilis reported in 2017.
"People who have multiple sexual partners are at even higher risk and the survey found that they are less likely to use a condom every time," Stefanogiannis said.
Half of respondents had had sex by the time they were 17 years old - similar to results from the United Kingdom.
Nearly 60 per cent of those surveyed reported not using a condom every time when they had more than two sexual partners in the previous year.
The Ministry was looking at options on how it could support the increased use of condoms, Stefanogiannis said.
The survey also assessed the proportion of positive heterosexual relationships, where both men and women were equally willing to have sex.
While most respondents said they and their partners were "both equally willing" to have sex that first time, the survey showed significant differences for men and women.
For men, 96 per cent reported they and their partners were equally willing, compared to 84 per cent of women.
The survey also asked respondents if they had ever been made to have sex since they were 13 years old.
Again, there were significant gender differences, with 11 per cent of women reporting they had been made to have sex, compared to three per cent of men. In 17 per cent of cases this was with a stranger.
Stefanogiannis said this information would be useful for those providing sexual health services and sex education to young people, as well as informing policies aiming to reduce family and sexual violence.
• More than 10,000 people aged 15 years and over were surveyed between June 2014 and July 2015
• Half had had sex by the time they were 17 years old
• 20 per cent had had sex before they were 16 years old. Broken down by ethnicity this included 39 per cent for Māori, 21 per cent for European, 20 per cent for Pacific, and 4 per cent for Asian.
• 80 per cent of young people (16-24 years) used a condom the first time they had sex
• 84 per cent of women and 96 per cent of men said they and their partners were "both equally willing" to have sex that first time
• The likelihood of having sex with at least two people in the previous year falls with increasing age: 27 per cent of 16- to 24-year-olds had at least two sex partners in the previous year, compared to 15 per cent of 25- to 34-year-olds.
• Over half (57 per cent) of people who had at least two sexual partners in the previous year didn't use a condom every time they had sex.
• 11 per cent of women and 3 per cent of men had an incident of sex against their will in their lifetime (since they were 13 years old).
• On average, men are younger (15 years old) than women (18 years old) the last time they had sex against their will. In only 17 per cent of cases it was with a stranger.