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<b><i>Introduction:</i></b> The last decade has witnessed a resurgence of interest in the clinician’s subjectivity and its role in the diagnostic assessment. Integrating the criteriological, third-person approach to patient evaluation and psychiatric diagnosis with other approaches that take into account the patient’s subjective and intersubjective experience may bear particular importance in the assessment of very young patients. The ACSE (Assessment of Clinician’s Subjective Experience) instrument may provide a practical way to probe the intersubjective field of the clinical examination; however, its reliability and validity in child and adolescent psychiatrists seeing very young patients is still to be determined. <b><i>Methods:</i></b> Thirty-three clinicians and 278 first-contact patients aged 12–17 years participated in this study. The clinicians completed the ACSE instrument and the Brief Psychiatric Rating Scale after seeing the patient, and the Profile of Mood State (POMS) just before seeing the patient and immediately after. The ACSE was completed again for 45 patients over a short (1–4 days) retest interval. <b><i>Results:</i></b> All ACSE scales showed high internal consistency and moderate to high temporal stability. Also, they displayed meaningful correlations with the changes in conceptually related POMS scales during the clinical examination. <b><i>Discussion:</i></b> The findings corroborate and extend previous work on adult patients and suggest that the ACSE provides a valid and reliable measure of the clinician’s subjective experience in adolescent psychiatric practice, too. The instrument may prove to be useful to help identify patients in the early stages of psychosis, in whom subtle alterations of being with others may be the only detectable sign. Future studies are needed to determine the feasibility and usefulness of integrating the ACSE within current approaches to the evaluation of at-risk mental states.