Purpose. Our purpose was to determine the best sonographic and color Duplex predictors differentiating tubal ring of ectopic pregnancy and the corpus luteum cyst of pregnancy. Methods. Prospective study of 73 pregnant women with empty uterus and questionable adnexal cystic structure devoid of fetal pole or yolk sac were included in this study. All cases underwent comprehensive transvaginal ultrasonography. Each adnexal structure was evaluated for six specific sonographic and color Duplex characteristics: the echogenicity of the wall in comparison to the endometrium and ovary, the wall thickness and internal echotexture, percentage of wall circumference by flow and resistive index of the flow. Results. Thirty four of the 73 questionable adnexal structures were ectopic pregnancy, and 39 were corpora lutea. Hyperechoic wall than the endometrium had 100% specificity and positive predictive value for diagnosing ectopic pregnancy. Iso or hypoechoic wall than the ovary had 91.2% specificity and 90% positive predictive value for diagnosing corpus luteum. Solid or turbid contents are predictive for ectopic pregnancy in contrast to clear contents which was predictive for corpus luteum. RI of less than 0.4 had a specificity of 100% for diagnosing EP, and RI of more than 0.7 had a specificity of 96.4% for diagnosis of EP. There was no significant difference in extent of the flow between the two groups. Conclusion. Echogenic cyst wall than the endometrium, thick cyst wall with turbid or solid contents, as well as resistive index less than 0.4 or more than 0.7 are useful sonographic predictors for differentiating ectopic pregnancy from corpus luteum cyst.