To describe the clinical outcome of fetuses with the prenatal sonographic diagnosis of isolated micrognathia. A retrospective review of fetuses and infants with the prenatal diagnosis of isolated micrognathia for April 1990 to August 2001 was undertaken. Isolated micrognathia was considered if no other anatomic, growth, or amniotic fluid abnormalities were detected by a detailed ultrasound examination. Sources of outcome data included maternal and neonatal medical records, prenatal genetics records, and karyotype results. Fifty-eight fetuses with the diagnosis of micrognathia were identified. Fifteen fetuses (26%) had isolated micrognathia by prenatal sonogram. After neonatal examination, 14 of 15 were found to have at least one additional abnormality. Eleven had a cleft of the soft and/or hard palate. Seven (54%) of 13 live-born neonates had mild to severe airway obstruction that required intervention. Four (31%) of 13 experienced feeding difficulties of varying duration. Follow-up data were available for 1 to 10 years. Eight (62%) of 13 children are reported to be doing well. Five (38%) of 13 children are reported to have mild to severe developmental delay. If micrognathia is the only sonographic finding identified, physicians and families should be prepared for possible respiratory difficulty at delivery, the presence of a cleft palate, and/or developmental delay.