A male infant was born with cyclopian malformation associated with trisomy D. Patients with cyclopia could be classified tentatively into two etiologically different groups. Cyclopia in the first group is thought to be causally related to trisomy D, presumably, D1. The second group is comprised of the remaining cases of cyclopia resulting from other chromosomal aberrations, nongenetic factors, and single gene mutations. The main point of distinction between these two groups is the existence of extracephalic anomalies in the first group.