We report that a 30-year-old woman with mental retardation was referred for prenatal diagnoses during pregnancy. An ultrasound scan showed that the heart structure and function of the fetus were normal. Cytogenetic analysis showed that the female karyotype was 47,XX, t(17; 22) (q21; q11), +21. The woman's husband had a normal male karyotype and was phenotypically normal. During this first pregnancy, an amniocentesis, which was done at 19 weeks, revealed that the fetal karyotype was 46,XX, t(17; 22) (q21; q11). Fluorescence in situ hybridization testing of amniotic fluid gave a normal result for chromosome 21. The child was a phenotypically normal female baby.