The aim was to identify from empirical research that used quantitative or qualitative methods the reasons women give for having an abortion. A search was conducted of peer-reviewed, English language publications indexed in eight computerized databases with publication date 1996-2008, using keywords 'abortion' and 'reason' (Medline: 'induced abortion' OR 'termination of pregnancy' OR 'elective abortion' and 'reason'). Inclusion criteria were empirical research on humans that identified women's reasons for undergoing an abortion, conducted in 'high-income' countries. 19 eligible papers were found. Despite variation in methods of generating, collecting, and analysing reasons, and the inadequacy of methodological detail in some papers, all contributed to a consistent picture of the reasons women give for having an abortion, with three main categories ('Woman-focused', 'Other-focused', and 'Material') identified. Ambivalence was often evident in women's awareness of reasons for continuing the pregnancy, but abortion was chosen because continuing with the pregnancy was assessed as having adverse effects on the life of the woman and significant others. Women's reasons were complex and contingent, taking into account their own needs, a sense of responsibility to existing children and the potential child, and the contribution of significant others, including the genetic father.