Background <p>The main objective was to evaluate the psychometric properties of the OutPatient Experience Questionnaire for Child and Adolescent Mental Health Services (OPEQ-CAMHS) among patients aged 16 and above, with a secondary objective of developing a parsimonious set of items and a short version of the instrument for this age group.</p> Methods <p>A national pilot study was conducted with adolescents from outpatient CAMHS in Norway, testing a new digital, continuous measurement approach using a measurement instrument developed through a comprehensive methodological framework. The study assessed missing data, ceiling effects, factor structure, internal consistency, discriminant validity, and construct validity. A shorter version was derived from psychometric results.</p> Results <p>The pilot study included responses from 555 (46.3%) patients. Low proportions of missing or “not applicable” responses were found for 18 of the 20 items, and all items were below the ceiling-effect criterion. Two scales emerged: “structure and process”, and “outcome”, both meeting alpha criteria. Each individual item demonstrated a stronger correlation with its expected scale than with any of the other scales. Construct validity was confirmed through associations with relevant variables expected to be associated with patient-reported experiences, including self-reported current state and well-being. The results supported a six-item short version.</p> Conclusions <p>Psychometric testing confirmed data quality, internal consistency, and construct validity of OPEQ-CAMHS. The short version addresses respondent burden concerns and is now ready for broad implementation in Norwegian CAMHS and potentially in similar healthcare settings worldwide.</p>