Introduction Breast cancer prevalence is growing worldwide. Many factors, such as diet and lifestyle could be determinants of the incidence of breast cancer. Coffee has been extensively studied in relation to several chronic diseases because of its multiple effects in health maintenance and its elevated consumption. We studied the relationship between coffee intake and breast cancer risk in the SUN (Seguimiento Universidad de Navarra) prospective cohort. Materials and methods We evaluated 10,812 middle-aged, Spanish female university graduates from the SUN Project, initially free of breast cancer. Coffee consumption was assessed with a 136-item validated food-frequency questionnaire (FFQ). Incident breast cancer cases were confirmed by a trained oncologist using medical records and by consultation of the National Death Index. We fitted Cox regression models to assess the relationship between baseline categories of coffee consumption and the incidence of breast cancer during follow-up. We stratified the analysis by menopausal status. Results During 115,802 person-years of follow-up, 101 new cases of breast cancer were confirmed. Among postmenopausal women, more than 1 cup of coffee per day was associated with a lower incidence of breast cancer (HR 0.44; 95% confidence interval: 0.21, 0.92) in the fully adjusted model, compared to women who consumed one cup of coffee or less per day. We observed no significant differences in regard to premenopausal women. Conclusion Even though the number of cases was low, slight indications of an inverse association between coffee consumption and breast cancer risk among postmenopausal women were observed. Further longitudinal studies are warranted to confirm this finding.