We report a case of trisomy 13 with cystic hygroma and generalized hydrops fetalis diagnosed prenatally by routine ultrasound prior to genetic amniocentesis in a 34-year-old woman. Although fetal cystic hygroma is usually associated with a 45,X karyotype, this and other previous reports suggest that it may be seen in association with other chromosomal and nonchromosomal abnormalities as well. Thus, a diagnosis of Turner Syndrome should not be made on the basis of a cystic hygroma observed by prenatal sonography alone.