ObjectiveThis study determined the prevalence and factors associated with sexual dysfunction in breastfeeding women.DesignCross-sectional analytical study.SettingPopulation-based study of individuals living in the northeast region of São Paulo state, Brazil.ParticipantsFrom May to August 2017, 372 women aged ≥18 years were selected who gave exclusive, predominant or complementary breast feeding up to 23 months postpartum, and who did not have contraindications for the resumption of intercourse. Pregnant women, those diagnosed with mental health problems, users of medications that affect sexual function (antihypertensives, antidepressants or antipsychotics) and women unable to read or understand the instructions for the study were excluded.Primary and secondary outcome measuresThe breastfeeding women completed the Female Sexual Function Index, the EUROHIS-QOL 8-item index and a questionnaire to collect participants’ sociodemographic, clinical and interpersonal data. A bivariate analysis was performed, and variables with p values<0.20 were analysed by multivariate logistic regression.ResultsSexual dysfunction was present in 58.3% of the study population. Factors significantly associated with female sexual dysfunction (FSD) included placing a low importance on sexual intercourse (adjusted OR [AOR]=2.49, 95% CI=1.22 to 5.09), limited communication with the partner (AOR=2.64, 95% CI=1.43 to 4.86), decreased frequency of sexual intercourse (AOR=2.17, 95% CI=1.30 to 3.61) and low quality of life (AOR=2.23, 95% CI=1.33 to 3.74).ConclusionsThe prevalence of FSD appears with a great magnitude in breastfeeding women. The risk factors for sexual dysfunction are biopsychosocial and these findings may lead to improved counselling for prenatal and postnatal care.