We examined whether the interaction of resting frontal electroencephalogram (EEG) asymmetry and social behavior during peer play was related to the occurrence of maladaptive behavior in preschoolers. Two independent cohorts of children were observed interacting in same-age and -gender play quartets at 4 years of age. Each child was also seen individually for a psychophysiology session during which time measures of EEG activity were recorded. We found that highly sociable children who exhibited greater relative right frontal EEG asymmetry were more likely to exhibit externalizing problems than sociable children who exhibited greater relative left frontal EEG asymmetry. We also found that shy children who exhibited greater relative right frontal EEG asymmetry were more likely to exhibit internalizing problems than shy children who exhibited left frontal EEG asymmetry. These findings suggest that the pattern of frontal EEG asymmetry in combination with social behavioral style is a significant predictor of maladaptive behavior problems during the preschool period.