Four in ten teenagers aged 17 have not spoken to their parents about sex and relationships, according to a report by the Economic and Social Research Institute and the Health Service Executive.
The joint research analyses how those aged between 13 and 17 years old receive information on sex and relationships.
It also examines the role of the information in shaping sexual behaviours among Irish adolescents.
The study finds that 55% of those aged 13 reported they received relationships and sexuality education (RSE) at school, which increased to 92% for those aged 17.
The research found there was a significant variation in relationship and sexuality education across second-level schools.
Overall, 45% of those aged 13 years reported they had discussed sex and relationship issues with their parents. By age 17, that had increased to just under 60%.
The research finds that young people who had better-quality relationships with their parents were more likely to talk to them about sex and relationships.
The report notes "a clear gender divide" in reports of "ease of discussions" with parents about sex.
Young women found it easier to talk to their mothers, while young men found it easier to talk to their fathers.
However, nearly 60% of young men found it difficult or very difficult to talk to their fathers about sex.
At age 13, parents and family were the main source of information about sex, but at age 17, friends were the most commonly cited source at nearly 50%.
At age 17, nearly 25% of young men and 20% of young women cited the internet, TV, films and books as their main source of information.
Those who had poor-quality relationships with their peers were much more likely to rely on information from these sources.
At age 17, 33% of young people reported having had sexual intercourse. Nearly 25% of young people expressed regret over the timing that they first had sex.
This proportion was substantially higher among young women (31%) than young men (16%).
Nearly 90% of young people who had sexual intercourse reported using contraception when first having sex and young people who had discussed sex and relationships with their parents at age 13 were "significantly more likely" to have used contraception the first time.
In contrast, those mainly reliant on their friends as a source of information on sex had lower levels of contraceptive use at first.
The findings of the study show that the quality of relationship between parents and their children is a key determinant of whether discussions about sex and relationships take place, according to report co-author Anne Nolan.
"Initiatives to support parents in developing positive communication skills may be expected to have broader benefits in terms of discussions about sex and relationships."
Fellow co-author Emer Smyth said a significant group of young people are not receiving information or advice on sex from their parents, making school-based relationships and sexuality education all the more important.
"The findings support the current move towards considering sexual wellbeing as part of broader school efforts to support young people's wellbeing."
The Health Service Executive's Education and Training Manager from the Sexual Health and Crisis Pregnancy Programme Moira Germain says the research shows that not only can parents have a specific protective influence, "they can also help their child to develop all the attitudes, values and behaviours necessary for forming and maintaining healthy relationships, including, in adulthood, healthy sexual relationships".
Minister of State with responsibility for Public Health, Wellbeing and the National Drugs Strategy, Frank Feighan, will launch the report today.
