Background: Sexual and reproductive health education and services are often of poor quality in Indonesia and although sexual intercourse among adolescents is not socially accepted, a change of norms is observable, putting adolescents at risk to acquire unwanted health outcomes. Aim: To analyse associations of behavioural, sociodemographic and informational factors with engaging in sexual intercourse among never-married adolescents aged 15 - 24 in Indonesia and to analyse potential differences in age groups. Methods: Data from 19,649 never-married male and female adolescents who ever went to school, obtained from the 2012 Indonesian Demographic and Health Survey, was used for analysis. Multiple logistic regression was applied to test for significance separately and after adjusting for variables. Results: Among all adolescents, factors associated with engaging in sexual intercourse were: older age, male sex, ever drank alcohol, smoking and ever used drugs. After stratifying for age, the same associations were found for older and younger adolescents. Additionally, among younger adolescents (15 - 19 years), those from poorer households, with a higher educational level and those currently attending school were more likely to engage in sexual intercourse. Among older adolescents (20 - 24 years), those from poorer households and rural areas were more likely to engage in sexual intercourse. Conclusions: Interventions are needed to equip male adolescents, those who ever drank alcohol, were currently smoking or ever used drugs with sufficient knowledge and tools to make informed decisions. Further qualitative research is needed to investigate the behaviour of adolescents towards sexual intercourse more in depth.