Obese and lean lines of pigs were developed previously by genetic selection for thick and thin backfat thickness, respectively. A greater proportion of these obese than lean pigs survive to weaning. A cross-fostering experiment was designed to study neonatal piglet growth and to attempt to decipher some of the causes of the increased survival rate. At about 24 h postpartum, lean and obese sows were paired, the litters standardized to six pigs and three pigs from each sow transferred to a dam of opposite genetic line. The smaller birthweight of obese than lean piglets and the lesser growth of either obese or lean pigs raised on obese compared to lean sows were both observations that might support greater survival of lean rather than obese piglets. Positive factors that might contribute toward the greater survival of obese than lean piglets were the greater lipid content of milk from obese than from lean sows during the first 2 wk postpartum and possibly greater physiological maturity of obese than lean pigs at birth as reflected in greater hemoglobin, hematocrit, plasma protein and plasma albumin.