Chronic ectopic pregnancy is not precisely defined in gynecologic and sonographic texts. The diagnosis of this enigmatic clinical condition is frequently not made until laparotomy. In the present retrospective study, we evaluated the transvaginal sonographic findings of cases who were diagnosed as chronic ectopic pregnancy intraoperatively and/or postoperatively. The incidence of chronic ectopic pregnancy was found to be 20.3% (62/305) of all ectopic pregnancies. Of these 62 cases, 55 had transvaginal sonographic examination. On transvaginal sonographic examination, all 55 cases of chronic ectopic pregnancy had a complex adnexal mass with an empty uterus and only 18 (32.7%) had simple fluid in the pelvis/cul-de-sac. In the majority of cases (82.7%, n = 48), there was a non-homogeneous echo pattern within the adnexal mass. Of 55 cases, 30 had color Doppler flow examination, of whom none had color Doppler flow imaging on the wall of the mass or within the mass. There was a negative quantitative beta human chorionic gonadotropin (beta-hCG) assay (i.e. 0 mIU/ml) in only 4 cases. Based on this study, we concluded that chronic ectopic pregnancy is not a rare clinical entity and should be considered in differential diagnosis among patients presenting with an adnexal mass and an overt clinical picture. Transvaginal sonography is sensitive in diagnosing chronic ectopic pregnancy, but not specific. The combined use of transvaginal ultrasonography and beta-hCG assay increases diagnostic accuracy. However, it should be kept in mind that a negative beta-hCG value does not rule out chronic ectopic pregnancy.