Recently published reports of 54 subjects with the amniotic band syndrome (ABS) were reviewed, paying particular attention to internal anomalies. Evidence from the internal anomalies suggests that in most cases reviewed, damage occurred in a definable time period, probably prior to 26 days postconception and before the establishment of effective embryonic circulation. Most defects are explicable in terms of interference with neuropore closure, malmigration of cephalic neural crest tissue, and damage to the mesonephros consistent with local interference of the graded expression of organizational genes resulting in a local defect in the organization of the embryo.