Objective: The aim of this study was to assess for the first time the criterion validity of the semi-structured Diagnostic Interview for ADHD in adults (DIVA 2.0), and its concurrent validity in comparison with the Conners’ Adult ADHD Diagnostic Interview for DSM-IV (CAADID) and other ADHD severity scales, following the Diagnostic and Statistical Manual of Mental Disorders (4th ed.; DSM-IV) criteria. Method: A transversal study was performed on 40 out-patients with ADHD to check the criteria and concurrent validity of the DIVA 2.0 compared with the CAADID. Results: The DIVA 2.0 interview showed a diagnostic accuracy of 100% when compared with the diagnoses obtained with the CAADID interview. The concurrent validity demonstrated good correlations with three self-reported rating scales: the Wender Utah Rating Scale (WURS; r = .544, p < .0001), the ADHD-Rating Scale (r = .720, p < .0001), and Sheehan’s Dysfunction Inventory (r = .674, p < .0001). Conclusion: The DIVA 2.0 is a reliable tool for assessing and diagnosing Adult ADHD and is the only one that offers free online access for clinical and research purposes.