When it comes to sexuality and norms, young Indonesians are becoming more open. Concern about this is related to the rapid increase in HIV prevalence in Indonesia, especially in Papua and West Papua Provinces. While much research has been conducted among youth who have left school, little is known about senior high school students' sexuality and sexual practices in these provinces. Using qualitative and quantitative data, we explore perspectives on and experiences of sexuality, contraceptive use, unintended pregnancy and unsafe abortion among 1082 Year 11 students from 16 senior high schools in both provinces. Findings suggest that around 38.3% of students reported having had sexual intercourse and 36.5% of these having had their first sexual encounter before they were 15 years old. Furthermore, contraceptive use among sexually active students was very low. Around 32% of female students who reported having had sexual intercourse also reported having an unintended pregnancy and the majority of them had had unsafe abortions. The paper points to the implications of students' high-risk sexual behaviours for HIV prevention.