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Records for over 10,000 litters farrowed at experiment stations in eight midwestern states cooperating in the former Regional Swine Breeding Laboratory were analyzed. Litters included were farrowed from the mid 1940's to the early 1960's. Over 7,000 litters, on test to 154 days, averaged 71.8% of pigs born alive surviving to weaning at 56 days and 66.3% surviving to 154 days, while 93.5% of those alive at weaning survived to 154 days of age. Stations, years and seasons showed variable influence on survival rate to weaning in the different states, but year × season interaction had a highly significant effect in each state tested. Males averaged about 30 g heavier at birth than females of the same litters. However, females had a significantly higher survival rate, from 5 to 9% above males. Survival rate of pigs of either sex rose significantly with higher birth weight. In addition, above-normal birth weight apparently had no detrimental effect on pig survival. Highest survival rates occurred in litters of 8.6 pigs born alive.