In the first 3 months of life, crying and fussing in normal infants tend to increase until 6 weeks of age and decrease progressively thereafter. To determine whether feeding choice and early infant temperament are predictors of early crying, 374 healthy, full-term infants were observed prospectively from birth to 6 weeks of age. Feeding choice and sociodemographic characteristics were ascertained in the first few days postpartum. Parents completed a 17-item early infant temperament questionnaire at 2 weeks of age and a 24-hour behavior diary for 8 days at 6 weeks of age. Initially breast-fed infants cried and fussed more frequently throughout 24 hours compared with those who were formula fed, and increased frequency and duration of crying and fussing were predicted by "more difficult" temperament. Furthermore, a different pattern of crying and fussing within the day was found for infants who were changed from breast- to formula feeding. However, according to stepwise multiple regression models, daily duration of crying/fussing was significantly predicted only by the temperament score (but not initial feeding choice), which accounted for 7% of the variance. Frequency of crying/fussing were predicted only by socioeconomic status, temperament, and feeding frequency, which accounted for 12% of the variance. Breast- or formula feeding at 6 weeks of age was independently associated with crying/fussing only during the evening. It was concluded that early infant temperament predisposes to early crying and fussing but is of limited use as a clinical predictor. Later crying/fussing behavior is not predicted by initial feeding.(ABSTRACT TRUNCATED AT 250 WORDS)