We investigated the causes of stunting and wasting using nationally representative data on preschool children from India (2005-2006, N = 41,306) and Guatemala (2008-2009, N = 10,317). We estimated stunting and wasting using the 2006 WHO standard and the 1976 WHO/National Center for Health Statistics (NCHS) reference. India and Guatemala had high levels of stunting; wasting was common in India but rare in Guatemala. Use of the WHO standard (based on breast-fed children) increased the prevalence of stunting in both countries but dramatically changed the pattern of wasting by age in India. In Indian children 0-5 mo of age, wasting more than tripled, from 8% to 30%, leading to the highest prevalence of wasting. Using the NCHS reference, the lowest and highest prevalence among Indian children occurred in children 0-5 and 12-23 mo, respectively. Also, we showed that household wealth and the condition of women were related to both stunting and wasting; review of the literature on wasting failed to identify factors that were not also related to stunting (e.g., seasonality, infections, and intrauterine growth retardation). Possible explanations for high levels of wasting in India include the poor status of women, the "thin-fat" infant phenotype, chronic dietary insufficiency, poor dietary quality, marked seasonality, and poor levels of sanitation. Use of the WHO standard calls for urgent attention to improving prenatal and infant nutrition and uncovers an alarming level of wasting in the young infant in India that use of the NCHS growth reference (based on bottle-fed infants) had masked.