Autopsy studies have shown that the fetal liver is more severely affected than the brain in asymmetric fetal intrauterine growth retardation (IUGR). This "brain-sparing" concept has led to the suggestion that ultrasonic measurements of biparietal diameter (BPD) are of limited value in detecting IUGR since the BPD is an indirect reflection of head and brain size. This study compares the effects of asymmetric and symmetric IUGR on newborn anthropometric measurements, including head circumference (HC), birth weight (BW), length (L), and ponderal index (Pl) in 33 growth-retarded infants divided into two groups, asymmetric (uteroplacental failure) and symmetric (maternal smoking, drug exposure, congenital anomalies, intrauterine infection), on the basis of the etiology of the IUGR. The percentage reduction in size from mean values for the same gestational age was calculated for each parameter. None of the newborn parameters were useful in distinguishing between infants with asymmetric and those with symmetric IUGR. Particularly noteworthy is the fact that the percentage decrease in HC was similar in both groups. Therefore, the concept of absolute "brain sparing" in asymmetric IUGR is erroneous, and ultrasonic measurements of BPD should be of value in detecting this form of IUGR.