Background More than 20 million invasive procedures are performed annually in the United States. The vast majority are performed with moderate sedation or deep sedation, yet there is limited understanding of the drivers of sedation quality and patient satisfaction. Currently, the major gap in quality assurance for invasive procedures is the lack of procedural sedation quality measures. Objective To develop and validate a robust, patient-centered measure of procedural sedation quality, the PROcedural Sedation Assessment Survey (PROSAS). Design Through a series of interviews with patients, proceduralists, nurses, anesthesiologists, and an interactive patient focus group, major domains influencing procedural sedation quality were used to create a multipart survey. The pilot survey was administered and revised in sequential cohorts of adults receiving moderate sedation for GI endoscopy. After revision, the PROSAS was administered to a validation cohort. Setting GI endoscopy unit. Patients A expert panel of proceduralists, nurses, and anesthesiologists, an initial survey development cohort of 40 patients, and a validation cohort of 858 patients undergoing sedation for outpatient GI endoscopy with additional surveys completed by the gastroenterologist, procedure nurse, and recovery nurse. Main Outcomes and Measurements Survey characteristics of the PROSAS. Results Patients were able to independently complete the PROSAS after procedural sedation before discharge. Of the patients, 91.6% reported minimal discomfort; however, 8.4% of patients reported significant discomfort and 2.4% of patients experienced hemodynamic and/or respiratory instability. There was a high correlation between patient-reported intraprocedure discomfort and both clinician assessments of procedural discomfort and patient recall of procedural pain 24 to 48 hours post procedure (P < .001 for all), suggesting high external validity. Limitations Single-center study, variability of sedation technique between providers, inclusion of patients with chronic pain taking analgesics. Conclusions The PROSAS is a clinically relevant, patient-centered, easily administered instrument that allows for standardized evaluation of procedural sedation quality. The PROSAS may be useful in both research and clinical settings.