Measurements of crown-heel length, head circumference, and birth weight were made on a large number of newborn infants. Birth weight by itself was frequently not a valid measure of fetal growth impairment. By including measurements of body length and head size along with birth weight, four distinct patterns of fetal growth impairment were identified. The four patterns included infants who had abnormally short body lengths for dates, infants who had evidence of disproportionate growth between body length and head circumference, infants who accumulated excessive amounts of soft-tissue mass, and infants who accumulated too little soft-tissue mass. Criteria for diagnosing each pattern were obtained prospectively and have been presented with allowances made for the effects of race, sex, fetal age, and parity on each pattern. The separate identification of the four patterns provided a more precise description of fetal growth impairment than could be obtained from birth weight and calculated gestational age.