We studied dietary composition and seasonal dietary patterns of the Méxican Twelve-lined Whiptail (Aspidoscelis lineatissima) in Chamela, Jalisco, México. We removed stomach contents and identified them as to the order to which they belonged. We calculated an importance value, food niche breadth, and food niche overlap indexes. Termites were the most important prey item. They were consumed throughout the year, particularly during the dry season, suggesting that A. lineatissima is a facultative specialist during the driest period of the study. Other important food items were lepidopteran larvae, coleopterans (adults and larvae), hymenopterans, orthopterans, and arachnids. Dietary composition was similar between the sexes. However, we found dietary differences among lizard size classes and seasons, indicating opportunistic use of temporally abundant arthropods.