A semi-structured interview was developed for classification of seizures in accordance with the 1981 International League Against Epilepsy (ILAE) criteria. The interview was administered over the telephone by trained lay interviewers. Interview-based diagnoses for 50 patients were compared with independent diagnoses by neurologists who also use the ILAE system for seizure classification. Interview diagnoses agreed with those of physicians for broad seizure-type classifications (i.e., partial vs. generalized onset) in 88% of patients and for detailed combinations of seizure type in 64% of patients. Nonchance agreement between the two sources, assessed by the kappa statistic, was excellent for any partial onset (kappa = 0.83), secondarily generalized (kappa = 0.81), and primary generalized tonic-clonic (kappa = 0.76) seizures. Agreement was fair to good for any generalized onset (kappa = 0.70), simple partial (kappa = 0.56), complex partial (kappa = 0.54), and generalized nonconvulsive (kappa = 0.56) seizures. Sensitivity ranged from 0.60 to 1.0 for partial onset seizures, and from 0.43 to 0.67 for generalized onset seizures. Specificity ranged from 0.60 to 0.87 for partial onset seizures, and was 1.0 for generalized onset seizures. Positive predictive value was 0.95 for any partial onset and 1.0 for any generalized onset seizure. These results suggest that this interview can produce accurate diagnoses of major seizure categories. Use of this instrument for clinical epilepsy research should facilitate conduct of large studies at a significant saving of both time and money.