Background Insertion deletion (I/D) polymorphism (rs4646994) in the angiotensin-converting enzyme (ACE) has a substantial effect on coronary heart disease (CHD). The amplification of an Alu repetitive element in an intron of the ACE has shown three potential genotypes of I/I and D/D as homozygous, and I/D as heterozygous.Objective The objective of this study was to investigate the association between the ACE gene polymorphism and CHD among male Iraqi patients with and without type2 diabetes mellitus (T2DM). Methods A case-control study of total 217 male subjects participated in this study, divided into three groups; Group 1 including 86 CHD patients with T2DM, group 2 including 78 CHD patients without T2DM, and group 3 including 53 age and sex-matched healthy individuals (as a control group). Genotyping of ACE (I/D) gene was performed using polymerase chain reaction (PCR) technique. ResultsThe II allele was significantly more frequent in CHD patients without T2DM compared to the control population, but not from those patients with T2DM (p < 0.05). Nonetheless, the ID allele was significantly more frequent in each of CHD with T2DM and control populations compared to the CHD without T2DM. The DD allele was significantly more frequent in CHD patients with T2DM compared to each of CHD patients without T2DM and control populations (p < 0.05). Conclusion We conclude that the D/D and I/D genotypes are implicated as risk factors for development of CHD with T2DM, but not CHD without T2DM among the male Iraqi population. However, larger sample sizes are needed to monitor the CHD patients and to validate this study.