Birth and first-48-hr death records were analyzed for 10,024 liveborn infants in Mexico City and 12,786 liveborn infants in Santa Cruz, Bolivia. The objective of the analysis was to characterize the early postnatal mortality rates for different types of fetal growth retardation and prematurity. Infants who were delivered prior to 37 weeks of gestation had 23–100 times the mortality risk of infants born at full term and normal weight. Light-for-gestational-age infants (birth weight <2,900 g) were further divided into proportionately growth-retarded with normal Rohrer's index (weight/height3) and disproportionately growth-retarded with low Rohrer's index. The proportionately growth-retarded infant had nearly twice the mortality of the full-term, appropriate-weight infants, whereas the disporportionately growth-retarded infants had 2.9–5.7 times the mortality rate of the full-term, appropriate-weight infants. There were some differences between samples in mortality rates and prevalence of the different classes of small infants, but the pattern of mortality within samples was consistent between samples.