OBJECTIVES: As a disease characterized by pain, Patient-Reported Outcomes (PROs) are important for determining disease severity and evaluating the efficacy of endometriosis treatments. In the absence of existing PROs that comply with the FDA PRO Guidance, two new PROs have been developed:  The Endometriosis Symptom Diary (ESD) and Endometriosis Impact Scale (EIS). The content validity of these instruments has been demonstrated by extensive qualitative and quantitative research with women with endometriosis. The first investigations of the reliability and validity of scores derived from the ESD and EIS are presented herein. METHODS: Women with surgically-confirmed endometriosis (n=268) in the US and Germany participated in a 12-week non-interventional study. A range of PRO measures were completed by participants throughout the study using an electronic handheld device, including: ESD, EIS, Biberoglu & Behrman Scale, Endometriosis Health Profile-30, Patient Global Impression of Severity and Change measures and single-item pain numerical-rating and visual analogue scales. Pre-specified analyses were conducted to evaluate the test-retest reliability, convergent validity, known-groups validity and responsiveness of scores derived from the ESD and EIS.   RESULTS: Intraclass correlation coefficients among participants classified as ‘stable’ support the test-retest reliability of ESD/EIS scores. Correlations between scores for the ESD/EIS and concurrent measures were consistent with a priori hypotheses, demonstrating convergent validity. Furthermore, Analysis of Covariance models revealed statistically significant (p<0.05) differences in ESD/EIS scores among participants of varying levels of symptom severity (as determined by scores on concurrent measures). Finally, observed ESD/EIS score changes in participants whose clinical status had improved (according to scores on concurrent measures) were significantly greater than those who had not improved/changed, providing evidence of responsiveness. CONCLUSIONS: Findings support the reliability and validity of scores derived from the ESD and EIS. Future research will seek to explore definitions of meaningful change in ESD/EIS scores using data from clinical studies.