OBJECTIVE To evaluate endocervical and vaginal environment changes in women using a levonorgestrel-releasing intrauterine system (LNG-IUS). METHODS A quasi-experimental study included sixty women who had an LNG-IUS inserted in the Family Planning Clinic of UNICAMP between April and November of 2016. Women in reproductive age, non-pregnant, without the use of antibiotics and contraceptives seeking for LNG-IUS insertion were selected for this study. All women were evaluated with regard to vaginal and endocervical pH, vaginal and endocervical Gram-stained bacterioscopy, and Pap-smear before and two months after LNG-IUS insertion. Clinical aspects such as cervical mucus, vaginal discharge, and cervical ectopy were also observed. RESULTS After LNG-IUS insertion, there was an increase in the following parameters: endocervical pH>4.5 (p=0.02), endocervical neutrophil amount (p<0.0001), vaginal cytolysis (p=0.04). There was a decrease in vaginal discharge (p=0.01). No statistically significant changes were found in vaginal pH, neutrophils amount in the vaginal mucosa, vaginal discharge appearance, vaginal candidiasis, bacterial vaginosis, vaginal coccobacillary microbiota, cervical mucus appearance, or cervical ectopy size. CONCLUSIONS Short-term LNG-IUS use did not increase vulvovaginal candidiasis or bacterial vaginosis, and led to diminished vaginal discharge. Notwithstanding, this device promoted reactional changes in the vaginal and endocervical environment, without modification on cervical ectopy size.