We examined the effect of anterior temporal lobectomy on cognitive function in the treatment of intractable partial complex seizures in a sample of 142 patients. Our current results replicate previous work in this area and clearly establish the presence of differential effects on cognitive function as a consequence of the side of the operation. Learning and memory are most susceptible to impairment postoperatively, although general intellectual abilities are also affected in a small number of patients. The data are further analyzed in a manner that permits determination of the probability of cognitive alterations postoperatively for individual patients. Information is provided to assist health-care professionals in evaluating the risk-to-benefit ratio relative to cognitive abilities as they consider this treatment alternative for their patients who suffer from intractable partial complex seizures.