Abdominal pregnancy is a rare condition defined as an ectopic pregnancy that implants in the peritoneal cavity and is associated with important morbidity and mortality. We report a case of a 35-year-old woman with an ultrasonographic diagnosis of a left extrauterine pregnancy located proximally in the isthmus or distally in the interstitial region. In the exploratory laparotomy a gestational sac implanted anteriorly on the uterine serosa was found, with no signs of uterine perforation or tubal abortion. The pathologic examination confirmed the diagnosis of an early first trimester abdominal pregnancy. This case illustrates the importance of an early sonography in the diagnosis of an abdominal pregnancy as well as a high index of suspicion.