The association between the polymorphism of the angiotensin-converting enzyme (ACE) gene and breast cancer risk has been extensively studied, however, the studies about the prognostic factors and ACE gene polymorphism are limited in number. Our aims were to analyze the distribution of the insertion/deletion (I/D) polymorphism of the ACE gene in Turkish premenopausal patients with breast cancer, which is more aggressive than the postmenopausal counterpart, and to assess whether DD genotype is associated with poor prognostic factors. The DD genotype has been shown to be associated with the increased serum and tissue levels of ACE, compared to those in II and ID genotypes. ACE genotypes were determined by polymerase chain reaction in 44 Turkish premenopausal patients with breast cancer and in 46 age-matched healthy premenopausal women. ACE genotypes are distributed in patients and control subjects as follows; DD is present in 25 (56.8%), ID in 17 (38.6%), and II in 2 (4.5%) patients, and DD in 28 (60.9%), ID in 12 (26.1%), and II in 6 (13.0%) healthy subjects, respectively. D and I alleles were found in 76.1% and 23.9% of the patients, while 73.9% and 26.1% in healthy subjects, respectively. In breast cancer patients, no significant association was observed between the ACE genotypes and poor prognostic factors, such as negative hormone receptor status, histological grade, lymph node involvement, higher number of lymph node metastases, and c-erb B2 overexpression, except that tumor size greater than 2 cm is associated with DD genotype (p = 0.02). Thus, ACE may influence the local tumor growth of breast cancer in premenopausal patients.