BACKGROUND: Breast cancer is the most common cancer in women worldwide and the cause of 20% of deaths from cancer in women. Every year about 2800 new cases of breast cancer are diagnosed in Croatia. It is very important to diagnose breast cancer at an early stage for a better treatment outcome. ----- AIM: The purpose of this study is to retrospectively evaluate the impact of COVID-19 pandemic on the treatment of patients with newly diagnosed breast cancer in Clinical Hospital Dubrava. Comparison of 2019, before COVID-19 pandemic and 2020. ----- MATERIALS AND METHODS: The retrospective study included 319 women with core needle biopsy or surgical biopsy proven malignant breast tumour in Clinical Hospital Dubrava whose data were extracted from the hospital database . We compared the number of patients, tumor size, waiting time for surgery, and the proportion of radical and conserving breast surgeries, as well as the proportion of axillary lymph node lymphadenectomy and sentinel lymph node biopsy. ----- RESULTS: The study included 319 patients, of which 213 belonged to the group 2019, and 106 patients 2020. The difference in the number of patients was statistically significant, and was conditioned by the extent of the hospital's work due to the COVID 19 pandemic. Although fewer patients were treated in 2020, they had shorter waiting times for surgical procedures. The difference in waiting times for surgery in 2019 and 2020 was statistically significant. The median length of waiting for surgery in 2019 was 28 days, and in 2020 it was 19 days. There was no significant difference between the proportion of radical and conserving breast surgeries and the proportion of axillary lymph node lymphadenectomy and sentinel lymph node biopsy. The average tumor size is higher in 2019 (1.82 cm) compared to 2020 (1.71 cm), but the proportion of tumors larger than 3 cm was higher in 2020. No statistically significant difference in tumor size was found. ----- CONCLUSION: This study showed that the COVID-19 pandemic had a significant impact on reducing the number of patients diagnosed and / or treated at Clinical Hospital Dubrava in 2020, which may be due to the reduced scope of clinical practice in the hospital due to the COVID-19 pandemic. The average tumor size in 2020 was smaller compared to 2019, but the proportion of tumors larger than 3 cm was higher. The proportion of radical and conserving operations, as well as the proportion of axillary lymph node lymphadenectomies and sentinel lymph node biopsies (SLNB) showed no significant differences. Group of patients who were treated in the Clinical Hospital Dubrava in a shorter interval in 2020 got timely and quality medical care. A comparison with 2019 shows that there were no delays with diagnosis and treatment, which can be seen through comparisons of the size of diagnosed cancers and the waiting time for surgical treatment. Moreover, it is noticeable that due to the organization of work focused only on the most urgent forms of treatment, the waiting time for surgical procedures has even decreased. Unfortunately, we cannot see the outcomes of treatment for patients in the period 2020 when the Clinical Hospital Dubrava was exclusively organized to work with COVID-19 patients, namely whether patients who were referred to other medical institutions in the Republic of Croatia had to wait longer for diagnosis and treatment.