Fifty-six women with endometriosis were examined for cul-de-sac endometriosis by ultrasonography and laparoscopy. Ultrasonographic cul-de-sac findings were classified into 3 groups; i.e. Group A (n = 21): no remarkable findings, Group B (n = 16): several nodular hyperechoic or cystic hypoechoic areas, and Group C (n = 19): multiple nodular or cystic areas and/or discontinuation of the contour of the posterior uterine wall. Laparoscopic cul-de-sac findings were classified into 3 groups; i.e. Group alpha (n = 6): no endometriosis, Group beta (n = 28): minimal or mild endometriosis, and Group gamma (n = 22): advanced endometriosis with or without cul-de-sac obliteration. Over-all coincidence of both findings was 50%. The rate of coincidence was significantly higher (p less than 0.05) in Group gamma (15/22) than in Group beta (9/28). This indicates that the diagnosis of minimal or mild cul-de-sac endometriosis by means of ultrasonography is difficult but that ultrasonography might be useful in diagnosing advanced cul-de-sac endometriosis.