Nine recent cases of coexisting intra- and extrauterine pregnancy at The Mount Sinai Medical Center are presented. The myriad of clinical presentations is exemplified in the postabortal, endometriosis, posttreatment; ovulation induction, and routine "rule-out ectopic" situations. A brief review of the literature follows detailing historical reports of diagnostic inaccuracy and delayed diagnosis. Several studies are cited supporting the difficulty of correctly diagnosing heterotopic pregnancy as well as factors which may predispose to it. The advantages and pitfalls of ultrasonography are mentioned as well as recommendations for early laparoscopic intervention when clinical history and ultrasound are suggestive. Caution is advised in those infertility patients who may undergo "routine" curettage at laparoscopy for ectopic pregnancy and thus, be at risk for inadvertent termination of an otherwise salvageable intrauterine pregnancy. This report further supports several other reviews in noting that the incidence of combined pregnancy may be much greater than formerly appreciated.