Polymorphisms of the progesterone receptor gene alter the expressions of two receptor isoforms involved in the regulation of progesterone's antiproliferative effect in endometriotic tissue. This study aims to identify the +331G/A polymorphism of the progesterone receptor gene in endometriosis patients in Palembang, South Sumatra. Identification of +331G/A single-nucleotide polymorphism (SNP) was conducted on 42 endometriosis patients through polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP). In this study, twenty-six (61.9%) subjects had heterozygous mutant genotype for the +331G/A SNP. No subject with homozygous mutant genotype for the +331G/A polymorphism was identified. The frequencies of polymorphic alleles for the +331G/A polymorphism was 30.9%. In conclusion, the +331G/A progesterone receptor gene polymorphism was present in endometriosis patients in Palembang, South Sumatra. This finding may warrant further studies to determine whether this polymorphism play a role in the development of endometriosis in the Indonesian population.