In 7 spontaneously aborted fetuses characterized by a large cystic hygroma in the nuchal region and a prominent and generalized edema, the structure and extension of the lymphatic system was studied. In all fetuses marked malformations of this system were found. Although the morphologic appearance seemed to vary greatly it is suggested that the disorder is essentially a generalized hypoplasia and partial agenesis of the lymphatic system, which ceases to extend peripherally at an early embryonic stage. A suggestion as to the mechanism of this growth inhibition is made.