Summary The title of Master`s thesis is: Quality of life and severity of symptoms of anxiety and depression in patients after mastectomy. Background Breast cancer is one of the most common malignancies in the Republic of Croatia. It is a public health problem around the world. There are various factors that cause breast cancer. In women with breast cancer, the presence of the BRCA-1 and BRCA-2 genes has been reported. Quality of life means physical and mental health. Self-assessment of quality of life is the most common measure used in medicine. In life when there is a negative impact on functioning, the quality of life declines. Numerous studies indicate that oncology patients have mental illnesses among their comorbidities. Anxiety and depressive disorders are the most common comorbidities. The treatment of breast cancer is multidisciplinary, combining surgical treatment, systemic treatment and radiotherapy. Aim The aim of this study was to investigate the relationship between quality of life and the occurrence and severity of anxiety and depressive symptoms after mastectomy. Methods The research was conducted on 120 respondents using a socio-demographic questionnaire and Croatian versions of the DASS-21 scale and WHOQOL-BREF questionnaire. The research required the approval of the Ethics Committee of the Croatian Catholic University. Results The results obtained show a greater severity of anxiety and depression symptoms in patients within one year of mastectomy than in patients who had mastectomy 5 years ago. The results show a negative impact of anxiety and depression on quality of life. Conclusion Patients with a shorter duration of diagnosis have more pronounced symptoms of anxiety and depression than patients who have a longer duration of diagnosis. The presence of pronounced anxiety and depression negatively affects the quality of life of patients after mastectomy.