We present the first reported case of prenatally diagnosed dup(22q) syndrome in a 20-year-old woman referred for genetic counseling because of a low maternal serum alpha-fetoprotein value. An ultrasound study at 22 weeks demonstrated oligohydramnios, intrauterine growth retardation, multiple facial malformations, and a cardiac defect. Fetal karyotype was 46, XYdup(22)(pter----q13:: q12----qter) by amniocentesis. Necropsy following pregnancy termination confirmed all prenatally delineated anomalies. Comparison is made with the complete and partial proximal dup(22q) syndromes. We emphasize the correlation between aneuploidy and the presence of low maternal serum alpha-fetoprotein, oligohydramnios, and midgestational intrauterine growth retardation.