Please cite this paper as: Gaudineau A, Ehlinger V, Nic Gabhainn S, Vayssiere C, Arnaud C, Godeau E. Use of emergency contraceptive pill by 15-year-old girls: results from the international Health Behaviour in School-aged Children (HBSC) study. BJOG 2010;117:1197–1204. Objective To describe emergency contraceptive pill (ECP) use and variation across countries/regions; and to explore personal and contextual factors associated with ECP use and differences across countries/regions. Design Data were obtained from 11 countries/regions in the 2006 Health Behaviour in School-aged Children cross-sectional study. Setting Data were collected by self-report questionnaire in school classrooms. Population The analysis is based on 2118 sexually active 15-year-old girls. Methods Contraceptive behaviours were compared across countries/regions by chi-square tests. Individual factors related to ECP use were investigated with separate logistic regression models. Multilevel random-intercept models allowed the investigation of individual and contextual effects, by partitioning the variance into student, school and country/region levels. Main outcome measures ECP use at last sexual intercourse. Results ECP use rate varied significantly across countries/regions. Poor communication with at least one adult (odds ratio [OR] 1.62 [1.12–2.36], P = 0.011) and daily smoking (OR 1.46 [1.00–2.11], P = 0.048) were independently associated with ECP use in comparison with condom and/or birth-control pill use. Sexual initiation at 14 years or later (OR 2.02 [1.04–3.93], P = 0.039), good perceived academic achievement (OR 1.69 [1.04–2.75], P = 0.035) and daily smoking (OR 1.63 [1.01–2.64], P = 0.045) were associated with higher levels of ECP use in comparison with unprotected girls. The country-level variance remained significant in both comparisons. Conclusions These data document the large heterogeneity in rates of ECP use between countries/regions. These differences could not be explained by individual or contextual factors, and raise further questions in relation to ECP access for adolescents and their education in its appropriate use.