To evaluate the role of speech manifestations in lateralization of temporal lobe seizures, we reviewed videotapes of 100 complex partial seizures in 35 patients who underwent temporal lobectomy for intractable epilepsy. All patients had prolonged electroencephalographic video monitoring with scalp and subdural electrodes, and their speech dominance was determined with an intracarotid amobarbital test. Speech manifestations were observed in 79 seizures and were classified as vocalization, normal speech, or abnormal speech. Vocalization of sounds without speech quality occurred ictally in 48.5% of patients. Normal speech (identifiable speech) occurred ictally in 34.2% of patients. Abnormal speech (speech arrest, dysphasia, dysarthria, and nonidentifiable speech) occurred in 51.4% of patients, either ictally or postictally. Of all the above speech manifestations, only postictal dysphasia and ictal identifiable speech had significant lateralizing value: 92% of patients with postictal dysphasia had their seizures originating from the dominant temporal lobe (p less than 0.001), and 83% of those with ictal identifiable speech had their seizures from the nondominant side (p = 0.013). This study shows that speech manifestations are common in complex partial seizures of temporal lobe origin and can provide an excellent clinical tool for lateralization of seizure onset.