A case of diprosopia anomaly in a blue shark (Prionace glauca) embryo from the South Atlantic Ocean is described. A detailed morphological description of internal organs was provided. The sample came from a pregnant female caught near Trindade Island (19°29'30"S, 028°20'00"W) in Southeast Brazil, with three normal embryos and one with external morphological abnormalities. The anomalous embryo was a male, with deformities in the skull and curvature of the spinal column twisted from the end of the first dorsal fin to the end of the caudal fin in a counterclockwise direction. Furthermore, two faces were observed, the right one with few alterations, while the left one was fused to it, with deformations in the eyes, mouth and nostril. The stomach was the only organ to show alteration in its shape, macroscopically. Organs of the digestive tract, renal structures and rectal gland was analyzed microscopically, and no alteration were observed in the samples. This is the first description of the internal organ of a specimen with diprosopia. These results suggest that, in addition to other factors, the survival of the embryo could be related to their ability to feed and escape predators in case to survive birth.