Context: Conception and abortion rates among women aged under-20 in Britain are high compared to those of other European countries. Conception and abortion rates among women aged under-20 are lower in France. In both countries, women from disadvantaged backgrounds are more likely to report a conception before age 20, and less likely to terminate the pregnancy with abortion if they do. A significant body of research has explored conception and abortion among young people in Britain, but fewer studies have capitalised on the potential of cross-national research to increase our understanding of the British situation. The aim of this research is to examine how proximal and contextual factors, particularly disadvantage, shape conception and abortion rates among under-20s by comparing two countries, Britain and France. Methods: Routinely-collected data on births and abortions are used to describe rates, trends, and area-level variation in conception and abortion rates within and between the two countries, and associations between disadvantage and conception and abortion at area-level. Nationally-representative survey data from both countries are used to examine differences between the two countries in behaviours and outcomes at each stage in the pathway to abortion (sexual activity, contraceptive use, pregnancy and recourse to abortion), and the associations with socioeconomic characteristics at each stage. Results: The proportion of young women sexually active is greater in Britain but differences between the two countries in contraceptive use are smaller. There are differences in the timing and circumstances of first sex between Britain and France. Associations between socioeconomic characteristics and each stage in the pathway to abortion in individual level analyses are similar in Britain and France. The correlation between disadvantage and conception and recourse to abortion is stronger in Britain. Discussion: The findings indicate that differences in conception rates between Britain and France are driven proximately by differences in the proportion of young women that is sexually active, and, to a lesser extent, differences in contraceptive use. Motivations to avoid pregnancy may play a key role in shaping behaviours at each stage of the pathway to abortion. A cross-national comparison has enabled the role of country-level social context to be explicitly examined. These empirical findings lend weight to arguments that differences in behaviour are shaped by nation-specific compositional and contextual factors including the level of social inequality and proportion of the population that is disadvantaged, the timing and pace of the transition to adulthood, prevailing norms relating to gender and young people’s sexuality and capacity for parenthood, and the opportunities that are available to, and perceived to be accessible by, young people.