We studied 92 secondary generalized tonic-clonic seizures (SGTCS) in 29 patients with a clearly lateralized seizure focus using video-EEG telemetry. An examiner, blind to the EEG, reviewed direction and type (forced versus nonforced) of head/eye deviation (HD). Forced HD consisted of sustained, unnatural tonic or clonic movements. Nonforced HD consisted of sustained deviations that were neither tonic nor clonic and were similar to volitional head movements. Eighty-three of the 92 SGTCS (26 of 29 patients) had lateralized and sustained HD. The direction of HD was contralateral in over 90% of seizures when the movement either (1) continued as the seizure generalized, or (2) occurred in the 10 seconds prior to generalization. The direction of HD was ipsilateral in over 90% of seizures if the movement ended before the seizure began to generalize (in all cases, the movement ended more than 10 seconds before generalization). HD occurring within the first 10 seconds after seizure onset was not of lateralizing significance. Forced HD was 89% contralateral, while nonforced HD was not of lateralizing significance. HD in SGTCS provides information on seizure focus lateralization.