Objectives. To determine appropriate indicators and age intervals for growth monitoring in this population, the relationship between monthly weight and length indicators and nutritional status at 12 months was evaluated among 102 low-income Peruvian infants. Methods. Cutoffs for defining adequate vs slow growth were obtained from published reference data, and sensitivities and specificities of each indicator were calculated. Results. Low weight gain in early infancy, especially from 1 to 2 months, is useful for predicting low weight at 1 year (sensitivity = 81%, specificity = 65%, 25th percentile cutoff). Use of actual weight at 2 months, however, produces comparable results (sensitivity = 86%, specificity = 57%, 50th percentile cutoff). Monthly length gains were weak predictors of low length for age. Neither weight nor length gains accurately predicted the opposite form of undernutrition. Nonhuman milk consumption before 4 months and poor appetite from 3 to 12 months were related to low early weight gain and subsequent undernutrition. Conclusions. Growth monitoring programs in this population should enroll infants at birth, monitor actual weight, promote exclusive breast-feeding and delayed introduction of nonhuman milk, and provide specific feeding advice to mothers of infants with frequently depressed appetites.