Although commonly encountered in spontaneous abortions, triploidy is rarely seen in fetuses surviving beyond mid-pregnancy. Mid-trimester sonographic findings in three triploid fetuses are described and compared with those reported in six prior cases. While sonographic characteristics are variable, common features include: 1) second trimester-onset fetal growth retardation with a reduced growth potential pattern of anthropometric growth, 2) body asymmetry with relative macrocephaly and an elevated head:abdominal circumference ratio, 3) hydrocephalus, 4) oligohydramnios, and 5) an abnormally large and/or hydropic placenta (in cases of paternal origin). Genetic amniocentesis and amniotic fluid chromosome studies should be performed when ultrasound findings suggestive of fetal triploidy are identified.