An insertion/deletion (I/D) polymorphism was identified in intron 16 of the gene encoding the human angiotensin I-converting enzyme (ACE), a candidate gene for chronic obstructive pulmonary disease (COPD). We investigated the relationship between this polymorphism in the ACE gene and the risk of developing COPD. Sixty-six COPD in-patients and 40 non-smoking control individuals were recruited for this study. The distribution of ACE genotypes in these individuals was studied. The frequencies of ACE genotypes were found to be 47.0% for DD, 30.3% for ID, and 22.7% for II in the COPD group and 32.5% for DD, 47.5% for ID, and 20.0% for II in the control group. The allele frequencies were found to be 0.62% for the D allele and 0.38% for the I allele in the COPD group and 0.56% for the D allele and 0.44% for the I allele in the control group. A significant difference was found between I and D allele frequencies (P < 0.05) of the study and control groups. Our results suggest that this ACE polymorphism may be associated with the development of COPD.