Previous analyses of the proposed cut-off score for the 18-item World Health Organization ADHD Self-Report Scale (ASRS-18) among psychiatrically referred adolescents have shown limited clinical utility. This prospective study examined the diagnostic accuracy and clinical utility of new cut-off scores of the ASRS-18 in a consecutive sample of 111 Swedish adolescent psychiatric outpatients. Using the Kiddie Schedule of Affective Disorders and Schizophrenia (K-SADS) as the reference standard and based on predefined sensitivity and specificity criteria, multiple new general and sex-specific cut-off scores were evaluated. Results showed that clinical utility was greater for sex-specific cut-off scores than for general cut-off scores. The greatest change in pre-test to post-test probability of ADHD diagnosis was observed with a balanced, high-specificity diagnostic cut-off score for girls, where the probability of ADHD increased from 40% pre-test to 82% post-test. The proposed new cut-off levels for the ASRS-18 are useful for the detection and identification of ADHD among adolescents in general psychiatric outpatient settings.© 2023 The Author(s).