Undernutrition in early childhood is associated with poor cognitive development and some changes in behavior. However, there is little information on their temperament. Our objective in this study was to determine whether undernourished children aged 6-24 mo had different temperament traits than better-nourished children. Two hundred and twelve undernourished children (weight for age < -2 Z-scores) attending community nutrition centers in 20 villages in rural Bangladesh and 108 better-nourished children (weight-for-age > or = -2 Z-scores) matched for age, sex, and village participated in the study. Temperament was assessed through an interviewer-administered maternal questionnaire consisting of 7 subscales: manageability, activity, emotionality, sociability, attention, soothability, and fear. After adjusting for significant covariates, the undernourished children were less sociable [regression coefficient (B) = -0.96; 95% CI = -0.04, -1.88], less attentive (B = -0.94; 95% CI = -0.19, -1.69), more fearful (B = 1.43; 95% CI = 2.44, 0.42), and had more negative emotionality (B = -1.08; 95% CI = 0.006, -2.16). In conclusion, these undernourished children had comprehensive differences in temperament traits, which may increase their risk of developing behavioral and mental health problems in later childhood.