PIP: Low birth weight (LBW) babies (2500 gm or less at birth) are more likely to die and suffer sequelae. Intrauterine growth retardation (IUGR) babies also weight the same, but they are born at 37 weeks or over. Small for gestational age (SGA) is a related term used for babies weighing less than expected. 20.6 million LBW babies were born in 1979, most of then in developing countries. In the US, 12.1% of nonwhites vs. 6% of whites had LBW babies in 1980 (50% of infant deaths were attributed to LBWs). A study in Guatemala showed that LBWs accounted for 88% of neonatal deaths. 15-21% of the US decline in neonatal mortality since the 1960s was due to birth weight distribution. 50% of the decline in Alabama was attributable to improved obstetrical care from 1970 to 1980. 12,000 Finnish children were followed up for 14 years, and those born with weights below the mean had significantly higher mortality than normal weight children. The saving of very LBW babies by medical technology has raised ethical questions, as many have mental and physical retardation and the expenses are enormous. SGAs have smaller stature IUGR/low ponderal index infants had 2.9-5.7 times the mortality of full-term normal infants, and they also had poorer academic progress, but IUGR/adequate ponderal index babies fared even worse. Such afflictions carry across generations, as evidenced by a Seattle study on 748 white women indicating impaired reproductive performance of female infants. Some of the components producing LBW are: maternal genetic, social, cultural, and nutritional factors, smoking, and dieting during pregnancy, wars and famines (e.g., Leningrad and Wuppertal during and after World War II). Anthropometric studies indicate that mothers with greater body size have larger babies, but genetics also play a role here. Intervention studies confirmed the importance of nutrition: in a Mexican study and increase of 180 gm of birth weight and 29.6% reduction of LBW was produced by supplementation during pregnancy. Ethnic differences in the development of the newborn are worth studying after discounting confounding factors.