With a prevalence of 19%, IDD appeared to be the commonest neuropsychiatric syndrome. The majority of the patients with IDD also had depressive and/or anxiety disorders. Quality of life, seizure control, and side effects to antiepileptic drugs were affected much more by depression or anxiety, than by IDD. The Danish version of IDDI has a poor reproducibility. The existence of IDD as a diagnostic entity is doubtful.