To develop and psychometrically evaluate the Endometriosis Treatment Satisfaction Questionnaire, a patient-reported assessment of satisfaction with endometriosis treatment. The Endometriosis Treatment Satisfaction Questionnaire was developed based on the results of five focus groups and three iterative sets of cognitive interviews along with expert opinion and a review of the literature. The psychometric properties were assessed using data collected during a multicenter, randomized, proof-of-concept trial. The development and validation processes followed the guidance recommended by the United States FDA for patient-reported outcome instruments. The Endometriosis Treatment Satisfaction Questionnaire's reliability, validity, and utility as a measure of patient satisfaction with their endometriosis treatment were supported. The results of the item-level analyses showed no evidence of distributional anomalies or response scale biases. The Endometriosis Treatment Satisfaction Questionnaire is unidimensional, has excellent internal consistency reliability, and discriminates well between known groups. Scores correlated well with other patient-reported outcome measures of endometriosis without being redundant. The Endometriosis Treatment Satisfaction Questionnaire has utility for assessing patient satisfaction with endometriosis treatment and may be useful in clinical trials that are assessing new treatments for endometriosis, especially when deciding between competing treatments or regimens that are found to have similar tolerability and efficacy.