An infant whose mother was a 17-year-old juvenile diabetic had the syndrome of phocomelic diabetic embryopathy (caudal dysplasia). The infant girl showed cleft palate, abnormal ears, renal abnormalities, and severe peromelia of the lower limbs with the left leg vestigial. Cases of phocomelic diabetic embryopathy have been recognized as a distinct syndrome only since 1964, and occur with prediabetic as well as diabetic mothers. A maternal metabolic defect more subtle than hyperglycemia may cause the caudal dysplasia. It may be similar to "insulin micromelia" produced in chickens by insulin injection of the incubating egg. On the other hand, alloxan diabetes in mice is associated with fetal limb abnormalities. It is not clear whether the human syndrome is related to maternal hyperglycemia or hypoglycemia, or to the direct influence of the insulin molecule.