Research Findings: Minor illnesses, such as upper respiratory infections, stomachaches, and fevers, have been associated with children's decreased activity and increased irritability. This multi-method investigation of 110 day care-attending children examined whether experience with recurrent, minor illnesses and negative emotionality worked together to predict young children's social functioning. Minor illness experience was assessed via weekly health screenings conducted by nurses. Toddlers' negative emotionality and social behavior were assessed using mothers' and fathers' reports. The two dimensions of negative emotionality and minor illness experience operated in different ways to predict children's functioning. Toddlers rated as more temperamentally angry displayed less social competence, especially when they also experienced high proportions of minor illness. Temperamentally fearful children exhibited more externalizing problems when they experienced a higher frequency of illness, whereas fearfulness was not associated with externalizing problems for children who were not frequently ill. Practice or Policy: Children's frequent experience with minor illnesses combined with negative emotionality appears to place toddlers at a heightened risk for exhibiting behavior problems. These findings have implications for child and family well-being as well as interactions with child care providers and peers within child care settings. Interventions could be developed to target "at risk" children.