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Weight, length, head circumference, skinfold thickness (triceps, biceps, subscapular, abdominal), and arm circumference were obtained within 72 hours of birth from 642 singleton, Caucasian infants born at 24-41 weeks gestation in Tucson, Arizona. Birthweights for term and preterm infants were similar to those reported for a comparable sea level population.From 24 to 41 weeks gestation skinfold thickness (SFT) increased at all sites from an average of 1.0 mm to 3.4 mm; arm circumference doubled; mid-arm cross- sectional fat area increased from 12 to 18 percent of the total cross-sectional mid­arm area; and the ratio of arm circumference/head circumference rose from 0.23 to 0.31. SFT measurements at the four sites were highly intercorrelated and without evidence of lateralization at birth. The rate of fat deposition, as assessed by change in median SFT, rose rapidly after 32 weeks gestation, peaking at 38-39 weeks and declining thereafter. These data may be helpful in determining nutritional status at birth and assessing postnatal growth of term and preterm North American infants.