The presence of gene polymorphisms of the estrogen receptors ERalpha (PvuII and XbaI) and ERbeta (AluI) in 61 women with endometriosis was investigated. A statistically significant correlation between PvuII ERalpha gene polymorphism (PvuII), both in homozygosity (PP) and in heterozygosity (Pp), and a recurrence of endometriosis was found. In conclusion, women affected by endometriosis with the ERalpha polymorphic allele, even if heterozygous, have a worse prognosis, and these results suggest that the ERalpha gene polymorphisms may be included among the genetic risk factors for endometriosis.