Breast cancer is the most common malignant tumor among population of women in the Republic of Croatia. According to the International Agency for Cancer indicators, Croatia is a country with a medium incidence and a high mortality rate of breast cancer. Besides environmental factors, there is also genetic component of disease. Knowledge about genetic component of breast cancer, genetic testing and genetic counselling is an important precondition for prevention. Women with genetic predisposition need intense supervision for the purpose of prevention, early detection of breast cancer or disease control. The aim of the study was to determine breast cancer patient’s knowledge about the illness, modalities of treatment and lifestyle. Study was conducted at the Department of Oncological Surgery, Clinic for Tumors, Clinical Hospital Centre Sisters of Mercy Zagreb, among 149 participants out of 235 hospitalized with breast cancer diagnosis (61.7%) in the year 2016. Results based on the nurse's anamnesis showed that 9.4% of breast cancer patients had no knowledge of their disease, 8.1% had no knowledge of modalities of treatment, and 6.8% of the lifestyle. There was no significant difference between the groups considering rural or urban residence. Nurse’s anamnesis questionnaire does not contain questions about knowledge of the genetic component of the disease. Data obtained in nursing anamnesis could be a guideline for better and higher quality of nurse’s work. The nurse can inform and educate breast cancer patients during their hospitalization, based on her knowledge about illness, treatment and lifestyle, and an especially important aspect is the information about the genetic component of breast cancer and possibility of genetic counselling and testing. The results indicate the need for extension and structuring of part of the nursing questionnaire related to patient knowledge.