Centromedian thalamic nuclei (CM) epileptiform EEG activities were recorded in patients with intractable partial motor, complex partial, and generalized seizures through implanted recording-stimulating electrodes, used for seizure control. CM epileptiform activities showed either little or no correlation to focal surface cortical and amygdaloid activities in patients with partial motor and complex partial seizures: CM paroxysmal discharges were correlated to focal epileptiform ictal activities only during the contraversive movements of partial motor and complex partial seizures. In contrast, CM epileptiform activities were consistently correlated to widespread surface cortical activities and clinical symptoms of fully developed nonconvulsive and convulsive tonic-clonic generalized seizures; i.e., unilateral CM double spike-wave complex discharges significantly preceded (p less than 0.001) the contralateral CM and bilateral surface cortical discharges and symptoms of nonconvulsive generalized seizures. Unilateral CM fast-slow-fast paroxysmal discharges significantly preceded (p less than 0.005) those of the contralateral CM and bilateral surface cortical regions and symptoms of the convulsive tonic-clonic generalized seizures. Individual spike-wave complexes from the frontal region preceded (p less than 0.001 and p less than 0.005) those at CM and other cortical regions during the nonconvulsive and clonic generalized attacks. No correlations between CM and cortical epileptiform activities were found, however, in the case of abortive, subclinical thalamocortical EEG discharges.