Uterine sacculation is rare complication affecting the pregnant uterus, and is difficult to diagnose. Sacculation consists of a transitory pouch or sac-like structure caused by inverted uterine polarity. Vaginal delivery is difficult, and even cesarean section can be difficult because of peculiar risks associated with uterine sacculation. We report a pregnant patient with posterior sacculation due to a huge myoma in the lower anterior uterine segment. Sacculation, especially that complicated by a huge myoma, is very difficult to accurately diagnose and makes cesarean section surgery challenging. Because of the myoma in our present case, opening the lower uterine segment was impossible with cesarean section. The uterus was instead opened by corporeal vertical cesarean section. Myomectomy was not performed and the giant myoma thus remained. Postoperative assessment revealed the uterus to still be retroverted. The giant myoma was the cause of sacculation in this case.