Of 2,958 pigs from a 320-sow, farrow-to-finish herd that were evaluated from birth to slaughter, 44 (1.5%) developed umbilical hernias. Hernias were detected mostly (34/44) when the pigs were between 9 and 14 weeks of age and were not fatal despite lack of treatment. Among littermates, weight gain prior to weaning was significantly (P = 0.04) lower in pigs that developed hernias (144.7 g/d) by 30 weeks of age than for nonaffected pigs (163.3 g/d), but growth rates from weaning to about 45 kg did not differ significantly. Records of pigs sired by 13 purebred boars were used to evaluate breed-of-sire associations. Pigs sired by American Spotted (n = 19; relative risk [RR] = 8.3; 95% confidence interval [CI] = 2.1 to 32.7) and Duroc boars (n = 378; RR = 2.1; 95% CI = 1.0 to 4.5) were more likely to develop umbilical hernias than were pigs (n = 1,644) sired by Yorkshire boars. Umbilical lesions (omphalitis or umbilical abscess) were associated (RR = 7.6; 95% CI = 1.2 to 49.5) with umbilical herniation on an individual basis, but the association was not evident (RR = 1.2; 95% CI = 0.2 to 7.6) when the litter was the unit of analysis. Analysis of sire associations, stratified by umbilical lesion status, indicated increased risks in the nonlesioned stratum for the American Spotted (RR = 8.7) and Duroc sires (RR = 2.2). Adequate comparisons of sire breed in the lesioned stratum could not be made, because umbilical lesions were an infrequent finding (9/2, 958).(ABSTRACT TRUNCATED AT 250 WORDS)