ABSTRACT OBJECTIVE To describe the prevalence of contraindicated use of combined hormonal contraceptives, progesterone-only contraceptives, and intrauterine devices in mothers participating in the 2015 Pelotas Birth Cohort according to the WHO medical eligibility criteria. METHODS The biological mothers of children belonging to the 2015 Pelotas birth cohort who attended the 48-month follow-up were studied. The 48-month follow-up data were collected from January 1, 2019, to December 31, 2019. Contraindicated use of modern contraceptives was considered to occur when these women presented at least one of the contraindications for the use of modern contraceptives and were using these methods. The prevalence of contraindicated use was calculated according to each independent variable and their respective 95% confidence intervals (95%CI). RESULTS The analyzed sample consisted of 3,053 women who used any modern contraceptive method. The prevalence of contraindicated use of modern contraceptives totaled 25.9% (95%CI: 24.4-27.5). Combined hormonal contraceptives showed the highest prevalence of contraindicated use (52.1%; 95%CI: 49.3-54.8). The prevalence of contraindicated use of modern contraceptives methods was greater in women with family income between one and three minimum wages, a 25-30 kg/m2 body mass index, indication by a gynecologist for the used method, and purchasing the contraceptive method at a pharmacy. The higher the women's education, the lower the prevalence of inappropriate use of modern contraceptives. CONCLUSION In total, one in four women used modern contraceptives despite showing at least one contraindication. Policies regarding women's reproductive health should be strengthened.