Standard temporal resection in the left hemisphere carries the risk of postoperative naming ability decline, especially with later epilepsy onset age/absence of hippocampal sclerosis. Language mapping has been performed routinely at some centers to minimize postoperative primary language impairment, but its effect on changes in naming performance has not been explored. This study examined naming outcome in 24 patients with nonlesional epilepsy who had left temporal resection after extraoperative language mapping. The mean decline in Boston Naming Test (BNT) score was 7.8, and 13 (54%) patients had a BNT decline greater than the Reliable Change Index. Simple correlations found significant relationships between BNT score decline and: later onset age, higher preoperative BNT score, and resection of isolated language sites. A multiple regression analysis showed that onset age was the best predictor of BNT decline. Although naming ability in patients with early onset age is stable with language mapping, there is still a risk of decline for those with later onset age.