In the assessment of adult attention‐deficit hyperactivity disorder (ADHD) symptoms, the diagnostic value of neuropsychological testing is limited. Partly, this is due to the rather low ecological validity of traditional neuropsychological tests, which usually present abstract stimuli on a computer screen. A potential remedy for this shortcoming might be the use of virtual reality (VR), which enables a more realistic and complex, yet still standardized test environment. The present study investigates a new VR‐based multimodal assessment tool for adult ADHD, the virtual seminar room (VSR). Twenty‐five unmedicated ADHD patients, 25 medicated ADHD patients, and 25 healthy controls underwent a virtual continuous performance task (CPT) in the VSR with concurrent visual, auditive, and audiovisual distractions. Simultaneously, head movements (actigraphy), gaze behaviour (eye tracking), subjective experience, electroencephalography (EEG), and functional near‐infrared spectroscopy (fNIRS) were recorded. Significant differences between unmedicated patients with ADHD and healthy controls were found in CPT performance, head actigraphy, distractor gaze behaviour, and subjective experience. Moreover, CPT performance parameters demonstrated potential utility for assessing medication effects within the ADHD population. No group differences were found in the Theta‐Beta‐Ratio (EEG) or dorsolateral‐prefrontal oxy‐haemoglobin (fNIRS). Overall, the results are very promising regarding the potential of the VSR as an assessment tool for adult ADHD. In particular, the combined assessment of CPT, actigraphy, and eye tracking parameters appears to be a valid approach to more accurately capture the heterogeneous symptom presentation of the disorder.