METHODS: Daily measurements of lung volume (functional residual capacity, FRC) were made during the perinatal period in eight infants (median gestational age, 37 weeks; range, 34 to 38 weeks) with abdominal wall defects. RESULTS: On the first day of life and before surgical intervention, four infants had FRCs below the reference range; the occurrence of low lung volumes was not significantly related to gestational age or diagnosis. Lung volume was further, but only temporarily, impaired by surgical closure of the abdominal wall defect, with a reduction in the median FRC from 25 mL/kg (range, 18 to 36) preoperatively to 12 mL/kg (range, 5 to 19) on the first postoperative day (P < .02). CONCLUSION: These data are consistent with abnormal antenatal lung growth in certain infants with abdominal wall defects.