The Medical Consultation Experience Questionnaire (MCEQ) is a new, brief self-report instrument that can be used with both adult patients and parents of child patients to assess two dimensions of people’s experiences interacting with medical practitioners: Alliance and Confusion. In contrast with existing measures, the MCEQ was expected to provide good discrimination across a full range of experience levels and to assess two distinct dimensions of experience with good factor validity. It was developed in a series of 7 preliminary studies (with 758 participants) and tested in 3 subsequent validation studies, which are the focus of the present report. Study 1 was an Internet sample of 199 parents of child patients, Study 2 was a hospital sample of 173 parents of child surgery patients, and Study 3 was an Internet sample of 204 adult patients. A confirmatory factor analysis specifying strict measurement invariance across the 3 groups produced a good fit. An item response theory analysis suggested that scales on the MCEQ provide good discrimination across a wide range of experience levels. The new scales measuring Alliance and Confusion each had a distinct pattern of convergent validity associations with criterion variables regarding alternate measures of consultation experience, treatment context, and patient-reported perception, behavior, and affect. Results support the validity of the MCEQ and suggest that Alliance and Confusion are two distinct and informative dimensions of medical consultation experience.