The diagnosis of early ectopic pregnancy remains challenging for the gynecologist. Although early detection of a suspected pregnancy has been facilitated by quantitative beta human chorionic gonadotropin studies and ultrasonography, a patient subgroup remains with an ambiguous presentation. In this group of patients, the clinician must rely on microscopic examination of products of conception in a uterine curettage specimen to rule out the presence of an extrauterine pregnancy. The presence of an implantation site, chorionic villi, or trophoblastic tissue in uterine curettage samples is conventionally held as definitive evidence of an intrauterine pregnancy. We present a series of four cases that challenge this convention. In these cases, chorionic villi or an implantation site were identified in uterine samples of pregnant women who each ultimately proved to have an ectopic pregnancy. If clinical suspicion is high, the finding of either chorionic villi or an implantation site should not preclude further workup of a possible ectopic pregnancy. In cases where only a few villi or a single chorionic villus are identified, other signs of intrauterine implantation such as intermediate trophoblastic cells, hyalinized vessels, and a fibrinoid matrix should be sought to establish firmly the diagnosis of an intrauterine pregnancy.