Endometriosis and leiomyoma display features similar to malignancy, requiring neovascularization to proliferation and growth. Altered vascular-related genes might be related to the development of endometriosis and leiomyoma. Polymorphisms of the angiotensin-converting enzyme (ACE) insertion/deletion (I/D) genes have been linked with some vascular diseases. This study investigates whether ACE I/D gene polymorphisms could be used as markers of susceptibility in endometriosis and leiomyoma. Women were divided into three groups: (1) endometriosis (n = 125); (2) leiomyoma (n = 120); (3) normal controls (n = 128). Genomic DNA was obtained from peripheral leukocyte. ACE I/D gene polymorphisms in intron 16 were amplified by polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) Genotypes and allelic frequencies in both groups were compared. We observed the genotype distribution and allele frequency of ACE I/D gene polymorphisms in both groups were significantly different. Proportions of ACE*I homozygote/heterozygote/D homozygote in both groups were: (1) 50.4/24/25.6%; (2) 25/23.33/51.67%; (3) 10.2/29.7/60.1%. Proportions of I/D alleles in each group were: (1) 62.4/37.6%; (2) 36.7/63.3%; (3) 25/75%. We concluded that ACE*I/D gene polymorphisms are associated with endometriosis and leiomyoma susceptibilities. ACE*I-related genotypes and allele are strongly related to the occurrence of endometriosis and moderately related to the occurrence of leiomyoma.