For decades, scholars have examined how children first recognize emotional facial expressions. This research has found that infants younger than 10 months can discriminate negative, within-valence facial expressions in looking time tasks, and children older than 24 months struggle to categorize these expressions in labeling and free-sort tasks. Specifically, these older children, and even adults, consistently misidentify disgust expressions as anger. Although some scholars have hypothesized that young infants would also be unable to categorize anger and disgust expressions, this question has not been empirically tested. In addition, very little research has examined developmental changes in infants' perceptual categorization abilities with high arousal, within-valence emotions. For this reason, the current study tested 10- and 18-month-olds in a looking time task and found that both age groups could perceptually categorize anger and disgust facial expressions. Furthermore, 18-month-olds showed a heightened sensitivity to novel anger expressions, suggesting that, over the second year of life, infants' emotion categorization skills undergo developmental change. These findings are the first to demonstrate that young infants can categorize anger and disgust facial expressions and to document how this skill develops and changes over time.