Sixty-three patients with intractable partial complex epilepsy were treated by anterior temporal lobectomy for seizure control. Psychometric studies before and after operation documented cognitive function and evaluated the effects of operation on cognition. The mean follow-up period was 7.7 months. Sixty-two of 63 patients had improved seizure control; 49 (78%) were seizure free. Operation had different effects on cognitive abilities in those with right vs. left temporal lobe excisions. Although both groups maintained summary IQ scores in the average range, after operation the left temporal group was less efficient on language-dependent cognitive tasks, particularly those that involved complex learning and memory. In contrast, persons who had right temporal ablations were either unchanged or slightly better cognitively after operation. Future research and clinical evaluations should focus on the components of the learning and memory processes when the ramifications of temporal lobe ablations on cognitive function are studied.