The aim of this prospective population-based study was to systematically define a cluster of diagnostic items which can assist in the early identification and classification of epileptic and non-epileptic seizures. A cohort of patients aged > or =14 years, suspected with a first epileptic seizure, were included in this study. A team of neurologists evaluated and classified all cases. Diagnostic items for epileptic and non-epileptic seizures were identified using logistic regression analysis. Three hundred and fifty cases entered this study. Distinctive features for epileptic seizures were postictal confusion (OR 0.09), an epileptiform EEG pattern (OR 0.02), and abnormal neuroimaging findings (OR 0.07), whereas for non-epileptic seizures of organic origin there was a history of hypertension (OR 7.5), and provoking factors (OR 13.4) such as exercise and warmth. Diagnostic items for seizures of non-organic origin were a history of febrile seizures (OR 5.8), treatment by a psychologist or psychiatrist (OR 9.1), and presentiment of the seizure (OR 3.7) such as a feeling of choking and palpitations. A separate analysis for the patients who were systematically investigated provided some additional diagnostic items for the different subgroups of patients. For instance, back arching during the seizure for the patients with seizures of non-organic origin and female sex for the patients with non-epileptic seizures of organic origin.