To describe the development, validation, and findings of a patient experience questionnaire across 7 types of residential and ambulatory mental health care services. Thirty-five items were hypothesized to cover information, participation, therapeutic relationship, personalized care, organization and collaboration, safety, patient rights, outcomes of care, and discharge preparation and after-care. Also included were 2 overall rating items (scoring and recommending the organization). This Dutch questionnaire was applied in 79 organizations in Belgium (N patients = 5,168). Exploratory structural equation modelling was conducted on a random split-half sample to examine dimensionality. Confirmatory factor analysis and multiple group confirmatory factor analyses were conducted on the holdout sample to confirm dimensionality and assess measurement invariance across type of service and patient characteristics. Multilevel logistic regression models linking subscale top box scores to overall rating items were used to assess criterion validity. The hypothesized dimensionality was partly confirmed, and configural and scalar invariance were demonstrated across types of organizations and patient characteristics. Subscale scores were significantly associated with overall ratings. Process evaluation showed that participating organizations strongly support continued use of this questionnaire. This validated patient experience questionnaire supports comparison across organizations from different types of services to improve the quality of mental health care.