Objective To evaluate the prevalence of functional ovarian cysts in users of two different types of contraceptive implants.Methods A total of 239 women were enrolled at 3 months of use of the etonogestrelreleasing implant (Implanon(R)) and the levonorgestrel-releasing implant (Jadelle(R)).Bimanual pelvic examination and vaginal ultrasound were performed during routine3, 6 and 12-month visits of asymptomatic women(control group). Women with ovarian cysts (or enlarged ovarian follicles ＞25 mm) (cysts group) were assessed weekly until disappearence or reduction of the image (including estradiol (E2) and progesterone measurement) and women with no ovarian enlargement underwent same evaluation for the same period of time.Results Ovarian cysts were detected in 5.1% and 13.0% of users of Implanon(R) and Jadelle(R), respectively, at 3rd month. At the 6th month of use, prevalences were 7.1%and 7.8%, and at 12th month rates were 25.7% and 14.7% in the two groups,respectively. E2 levels were significantly higher in cysts group than in control group.The time until disappearance of the ovarian cyst was similar in Implanon(R) and Jadelle(R)group. There were more cases of menorrhagia in patients rveth ovarian cysts than in patients with no ovarian enlargement.Conclusions The finding of ovarian cysts or enlarged ovarian follicles during the first year of use of Implanon(R) and Jadelle(R) implants is common and transient and should not be interpreted as a pathologic ovarian cyst. No further medical interventions are necessary.