Objective: To describe the occurrence of endometriosis in monozygotic
twins. Design: Postal questionnaire plus confirmation of disease statu
s. Setting: Twins were recruited via the American Endometriosis Associ
ation and the National Endometriosis Society of Great Britain and via
British gynecologists. Result(s): Fourteen twin pairs were concordant
for endometriosis, and two were discordant. Nine pairs of twins had mo
derate-severe endometriosis. Conclusion(s): These findings contribute
to the growing body of literature that suggests endometriosis has a ge
netic basis. (C) 1997 by American Society for Reproductive Medicine.