BACKGROUND: Sexual health education in the United Kingdom is of variable quality, typically focusing on the biological aspects of sex rather than on communication, relationships, and sexual pleasure. The Internet offers a unique opportunity to provide sexual health education to young people, since they can be difficult to engage but frequently use the Internet as a health information resource. OBJECTIVES: To explore through qualitative research young people's views on what elements of a sexual health website would be appealing and engaging, and their views on the content, design, and interactive features of the Sexunzipped intervention website. METHODS: We recruited 67 young people aged 16-22 years in London, UK. We held 21 focus groups and 6 one-to-one interviews to establish sexual health priorities, views on website look and feel, and what features of a sexual heath website would attract and engage them. Two researchers facilitated the focus groups, using a semistructured topic guide to lead the discussions and asking open questions to elicit a range of views. The discussions and interviews were audio recorded and detailed notes were made on key topics from the audio recording. Young people's views influenced design templates for the content and interactive features of Sexunzipped. RESULTS: Young people particularly wanted straightforward information on sexual pleasure, sexually transmitted infections and pregnancy, how to communicate with partners, how to develop skills in giving pleasure, and emotions involved in sex and relationships. Focus group participants wanted social interaction with other young people online and wanted to see themselves reflected in some way such as through images or videos. CONCLUSIONS: While it is challenging to meet all of young people's technological and design requirements, consultation with the target audience is valuable and necessary in developing an online sexual health intervention. Young people are willing to talk about sensitive issues, enjoy the discussions, and can offer key insights that influence intervention development.