en Original Article Original Article <strong>Background:</strong> Polycystic ovary syndrome (PCOS) is a heterogeneous complex genetic disorder characterized by hyperandrogenemia hyperinsulinemia insulin resistance and chronic anovulation. It is the most common endocrine disorder in women of reproductive age with an enigmatic pathophysiologic and molecular basis. Obesity hyperandrogenism and infertility occur frequently in PCOS which mostly have a genetic predisposition and are features known to be associated with the development of breast cancer risk.<br> <strong>Objective:</strong> In present study frequency of PCOS in patients with premenopausal breast cancer was compared with the frequency in women without breast cancer.<br> <strong>Materials and Methods:</strong> This is a case-control study which compared PCOS frequency in 166 patients with premenopausal breast cancer and 166 healthy controls with normal mammography in last 6 months.<br> <strong>Results:</strong> Eleven patients (6.62%) in case group and 16 patients (9.63%) in control group had polycystic ovary syndrome according to their questionnaire. The difference was not significant (p=0.645).<br> <strong>Conclusion:</strong> There was no relationship between frequency of polycystic ovary syndrome and breast cancer in this study. This might be due to the age of patients with breast cancer in this study which was mostly over 40. It could be significant if the patients were chosen in lower age for showing more effect of genetic than environment. The adjustment or matching of other risk factors could help to find the better results. Polycystic ovary syndrome, Premenopausal breast cancer, Endocrine disorder. 86 89 http://ijrm.ir/browse.php?a_code=A-10-549-185&slc_lang=en&sid=1 Nasrin Ghasemi Yes Department of Medical Genetics, Research and Clinical Centre for Infertility, Shahid Sadoughi University of Medical Sciences, Yazd, Iran Mohammad Reza Mortazavizadeh No Department of Oncology, Shahid Sadoughi Hospital, Shahid Sadoughi University of Medical Sciences, Yazd, Iran Aboolfazl Khorasani Gerdekoohi No Medical School, Shahid Sadoughi University of Medical Sciences, Yazd, Iran