To asses the validity of maternal reports of poor infant appetite, these histories were compared with measured energy consumption on 1621 d of observation of 131 Peruvian infants in a low-income community. Mean (±SD) total energy intakes on days with reported anorexia were 338 ± 88 kJ/kg body wt in infants 1-6 mo of age and 299 ± 92 kJ/kg body wt in infants aged >6 mo compared with 395 ± 92 and 342 ± 88 kJ/kg body wt in the respective age groups when appetites were reportedly normal (P < 0.001). Energy intake from non-breast-milk sources was more affected than energy from breast milk. The epidemiology of poor appetite was assessed in 153 infants who were monitored longitudinally during their first year of life. The prevalence of reported anorexia increased progressively from 22 to 317/1000 d of observation from <1 to 11 mo of age. Infant age and the presence of fever, diarrhea, and respiratory illnesses were each associated positively, and consumption of breast milk was associated negatively with the presence of reduced appetite. Poor appetite, rather than lack of food, may explain in part the low energy intakes by infants in this community.