The aim was to substantiate the putative significance of angiotensin-converting enzyme (ACE) (insertion/deletion) I/D polymorphism on prostate cancer risk, BTPSA-ATPSA (before treatment-after treatment prostate-specific antigen) levels and tumor development. Materials and Methods: 48 prostate cancer patients and 51 healthy volunteers were included. The ACE I/D genotypes were determined by PCR (polymerase chain reaction) and RFLP (restriction fragment length polymorphism) techniques. Results: The DD genotype may have detrimental and the II genotype may have protective effect on prostate cancer (p=0.03). The highest before treatment PSA (BTPSA) values were found in the patient group having the DD genotype (p=0.017). PSA-AT levels were higher in homozygous mutant DD than homozygous II and the decrease in PSA-AT level was found to be statistically significant in each genotype (p=0.000). Patients with the D allele showed a higher prevalence of late stage prostate carcinoma when compared to the patients with II genotype (p=0.022) and the detrimental effects of the D allele, both in lymph node metastases and distant metastasis were observed. Conclusion: The risk of prostate cancer development, the PSA level and tumor metastasis may be associated with genetic variation in the ACE AID genotypes which may be used as an important biomarker for further studies.