Large tumors removed from the lower abdomen and pleural cavity of a 24-year-old male Amerindian in Paraguay consisted mainly of multitudes of minute, proliferating, acephalic cestode larvae embedded in fibrous tissue. The parasite resembled Sparganum proliferum Stiles 1908 but was markedly less differentiated. From a review of the literature and examination of available reference material, it is concluded that in addition to the present one there are eight well documented cases of proliferating acephalic larval cestode infection in man: five in Japan and one in Florida (USA) that were S. proliferum, one in Pennsylvania (USA) that was an undifferentiated cysticercus or cysticercoid, and one in Taiwan that probably was an undifferentiated tetrathyridium. In four other cases the parasites are reclassified as being of doubtful nature in three and a racemose cysticercus in one. Review of the known species of proliferating cestode larvae naturally occurring in animals failed to identify possible sources of the acephalic forms observed in man.