The objective of this study was to perform a systematic review of the literature to determine whether there is an association between polycystic ovary syndrome (PCOS) and gynaecological malignancy. Medline and Embase databases (1968-2008) were searched to identify publications on the association between PCOS and gynaecological cancers including breast cancer. Studies were selected that examined the association between PCOS and all types of gynaecological malignancies. A total of 19 studies exploring the association between PCOS and breast, endometrial and ovarian cancer were identified. Of these, only eight could be included after review. The data showed variability in the definition of PCOS. A meta-analysis of the data suggests that women with PCOS are more likely to develop cancer of the endometrium (OR 2.70, 95% CI 1.00-7.29) and ovarian cancer (OR 2.52, 95% CI 1.08-5.89) but not breast cancer (OR 0.88, 95% CI 0.44-1.77). Women with PCOS appear to be three times more likely to develop endometrial cancer but are not at increased risk of breast cancer. There is insufficient evidence to implicate PCOS in the development of vaginal, vulval, cervical or ovarian cancers. The paucity of studies investigating the association between PCOS and gynaecological cancers is likely to affect the reliability of the conclusions.