A 5-year-old Swedish Red cow, pregnant for 465 days according to the last insemination record, was presented in this case. She conceived by artificial insemination at spontaneous estrus using frozen-thawed sperm of Swedish Red sire. No abnormalities were detected during gestation and no clinical signs of parturition at the expected time of delivery were noted. She was reexamined several times to eliminate breeding records error and, once prolonged gestation was confirmed, parturition was induced. The calf survived birth but died 10 min after birth. A macroscopically giant fetus was diagnosed. Following necropsy, some congenital anomalies were noticed. While the structure of the right adrenal gland was normal, disorganized soft tissue was observed in the left one, in which cortical and medullar regions could not be distinguished. The calf's pituitary gland was also normal. Thus, prolonged gestation was attributed to a case of unilateral adrenal gland dysgenesis.