Objective: To investigate the association of CTLA-4 gene microsatellite polymorphism with endometriosis and adenomyosis.  Methods: The polymorphic (AT)n repeats in the 3’untranslated region of exon-4 of CTLA-4 gene[CTLA-4(AT)n] was detemined by short tendem repeat polymerase chain reaction (STR-PCR) method in 56 cases of endometriosis patients , 31 cases of adenomyosis patients and 35 cases of controls, with primes 5’-GCC AGT GAT GCT AAA GGT TG-3’and 5’- AAC ATA CGT GGC TCT ATG CA -3’. The amplified products were electrophoresed by 8% polyacrylamid gel and followed by 0.1% silver staining. Some of the amplified products were sequenced directly.  Results: 12 alleles of the (AT)n repeats in the 3’untranslated region of exon-4 of CTLA-4 gene were found in endometriosis patients, 12 alleles in adenomyosis patients. The frequency of 120bp allele in endometriosis patients was significantly higher than that in adenomyosis patients and in controls(P0.05). The frequency of 120bp allele in the clinical stages of endometriosis was not significant difference(P>0.05).  Conclusion: Our findings suggest that the polymorphic (AT)n repeats in the 3’untranslated region of exon-4 of CTLA-4 gene is associated with endometriosis. CTLA-4(AT)n repeats 120bp may be the susceptible gene in endometriosis patients.