We performed a prospective study to evaluate the reliability of a rapid monoclonal antibody urine pregnancy test with a sensitivity limit of 20 mIU/mL combined with transvaginal ultrasonography in the early diagnosis of ectopic pregnancy in 116 women with subacute pelvic pain and a stable general condition. The diagnosis of tubal pregnancy was confirmed with laparoscopy in 100 of the 103 women with positive sensitive urine pregnancy tests and no intrauterine gestational sac at transvaginal ultrasonography. Laparoscopy revealed a hemorrhagic corpus luteum in four of the eight subjects with negative monoclonal antibody pregnancy tests and no intrauterine gestational sac, an ovarian cyst in three and a normal pelvis in one. Of the five women with a positive pregnancy test and an intrauterine gestational sac, two had a hemorrhagic corpus luteum, two a normal pelvis and one a tubal pregnancy at laparoscopy. The sensitivity of a monoclonal antibody urine pregnancy test and transvaginal ultrasonography combined for the diagnosis of ectopic pregnancy was 99%, and the specificity was 80%, with positive and negative predictive values of 97% and 92%, respectively.