Introduction: Breast cancer is the most frequently diagnosed cancer in Poland. It develops slowly, very often without any symptoms for a long time. The key element in the prevention of breast cancer, which affects the rate of incidence, is women’s knowledge of the disease and participation in screening tests. Aim: The purpose of this study is to assess the relationship between the prevalence and intensity of health behaviours and self-efficacy and the level of knowledge about breast cancer prevention in a group of professional nurses. Material and methods: The study involved 125 nurses employed at the St. John Paul II Hospital in Krakow. Standardised tools were used in the study: Generalized Self-Efficacy Scale (GSES), Health Behavior Inventory (HBI) and a self-designed questionnaire assessing knowledge about breast cancer prevention. Results: Nurses with higher education presented a higher level of knowledge regarding breast cancer prevention. Women with a high intensity of health behaviours in the preventive domain showed a better knowledge of breast cancer topics. Similarly, nurses characterised by a strong sense of self-efficacy presented a higher level of knowledge in this area. Conclusions: Almost half of the nurses surveyed presented a good level of knowledge about breast cancer prevention. The severity of health behaviours was rated as average, slightly higher in preventive behaviours and lower in terms of health practices. The stronger the sense of self-efficacy, the higher the level of knowledge and the higher the intensity of health behaviours.