Background: As part of the REPROSTAT2 project, this systematic review aimed to identify factors associated with teenage pregnancy in 25 European Union countries. Methods: The search strategy included electronic bibliographic databases (1995 to May 2005), bibliographies of selected articles and requests to all country representatives of the research team for relevant reports and publications. Primary outcome measure was conception. Inclusion criteria were quantitative studies of individual-level factors associated with teenage (13–19 years) pregnancy in EU countries. Results: Of 4444 studies identified and screened, 20 met the inclusion criteria. Most of the included studies took place in UK and Nordic countries. The well-recognized factors of socioeconomic disadvantage, disrupted family structure and low educational level and aspiration appear consistently associated with teenage pregnancy. However, evidence that access to services in itself is a protective factor remains inconsistent. Although further associations with diverse risk-taking behaviours and lifestyle, sexual health knowledge, attitudes and behaviour are reported, the independent effects of these factors too remain unclear. Conclusions: Included studies varied widely in terms of methods and definitions used. This heterogeneity within the studies leaves two outstanding issues. First, we cannot synthesize or generalize key findings as to how all these factors interact with one another and which factors are the most significant. Second, it is not possible to examine potential variation between countries. Future research ensuring comparability and generalizability of results related to teenage sexual health outcomes will help gain insight into the international variation in observed pregnancy rates and better inform interventions.