Abstract
Modern psychopathology classification systems position attention-deficit/hyperactivity disorder (ADHD) with different groups of conditions, either with externalizing or neurodevelopmental. As such, the optimal placement of ADHD in modern classification systems remains unclear. We advanced the literature by mapping ADHD symptoms onto three transdiagnostic psychopathology spectra-externalizing, neurodevelopmental, and internalizing-and their symptoms. ADHD symptoms had varied associations with different spectra, with subsets of symptoms relating most strongly to externalizing, others to neurodevelopmental, and still others to internalizing. Impulsivity, poor schoolwork, and low perseverance were most closely tied to externalizing, cognitive disengagement symptoms (e.g., confused, stared blankly, daydreamed) and immaturity were most closely tied to neurodevelopment, and cognitive disengagement symptoms were also tied to internalizing. Our findings advise against conceptualizing and treating ADHD as a unitary construct and against placing ADHD exclusively under either externalizing or neurodevelopmental spectra. Symptom-focused approaches will better inform modern psychopathology classification systems. (PsycInfo Database Record (c) 2024 APA, all rights reserved).