PurposeTo determine whether there are changes in sexuality after breast cancer, to better understand the sexual function of women with breast cancer, and to investigate the potential relationship between sexual dysfunction and socio-demographic and clinical variables.MethodsA cross-sectional study. This study included 514 women with breast cancer between 21- and 66-years-old. The cases were gathered between June 2016 and January 2017. The instruments used were the questionnaire on Women’s Sexual Function and a questionnaire to collect socio-demographic and clinical data.ResultsThe average age (± standard deviation, SD) of participants was 46.34 ± 8.28 years. Their average age at date of diagnosis was 42.26 ± 8.56 years, and the average time suffering from cancer was 4.05 ± 5.23 years. There were significant differences (p = 0.002) in the presence of sexual dysfunction before (32.1%) and after (91.2%) cancer. The primary sexual dysfunctions were due to penetration pain (50.6%), lubrication (50.6%), dysfunctional desire (44.6%), and dysfunctional excitement (44.6%). Two-thirds of participants were satisfied with their sexual relations. The women who presented most sexual dysfunction were those that had a bilateral mastectomy (p = 0.009) and those who received chemotherapy, radiotherapy and hormonal-therapy (p < 0.001).ConclusionSexual function was changed in women with breast cancer. The main problems included penetration pain, desire, lubrication, and dysfunctional excitement. It is important that Health professionals recognize which circumstances influence the sexual function of women with breast cancer and to make interventions that facilitate sexual adjustment.