The clinical manifestations and cytogenetic changes of a patient with 46,XY,del(8)(p21.1) are compared with those of nine other patients with a similar deficiency of chromosome 8. Patients with this chromosome anomaly have a syndrome of postnatal growth retardation, microcephaly, mental retardation, epicanthal folds, posteriorly angulated and malformed ears, short neck, relatively increased internipple distance, and congenital heart defect. A short and broad nose, a wide and flat nasal bridge, and a small jaw are observed in young patients but tend to become less apparent with increasing age. In most instances, the syndrome has been associated with a de novo chromosome abnormality. Levels of glutathione reductase in our patient were normal-a finding consistent with localization of the gene coding for this enzyme to the proximal part of band 8p21.1 if gene dosage studies are reliable.