The Schedule for Affective Disorders and Schizophrenia for School-Age Children-Present and Lifetime version (K-SADS-PL) is a valuable tool for diagnosing mental disorders in children and adolescents. Previous studies have examined its interrater reliability, but there is limited information on individual disorders, on the updated DSM-5 version. This study aims to analyse the interrater reliability of the Icelandic translation of K-SADS-PL, DSM-5 version. K-SADS-PL was administered to a clinical sample of outpatients from the Icelandic Anxiety Centre for Children, Adolescents, and Young Adults, and The Department of Child and Adolescent Psychiatry at Landspítali, the National University Hospital in Reykjavík, Iceland. In total, 135 patients aged 6–18 were included in this study. We assessed the interrater reliability using Cohen’s κ, with results ranging from poor to excellent (0.3–1.0), though most disorders showed excellent reliability (κ > 0.75). The Icelandic translation of the DSM-5 K-SADS-PL is generally reliable when used by properly trained post-graduate students, which supports its use in clinical settings.