Objective Streamlining the diagnosis is a key factor in improving the treatment outcomes for breast cancer. The aim of this study was to determine factors influencing time to seeking medical advice and treatment onset in women who are diagnosed with breast cancer in Serbia. Methods The study was a multicenter, cross‐sectional national survey, performed at 10 oncology centers in Serbia. Time intervals spent throughout the complex diagnostic pathway were evaluated using a validated questionnaire administered to women with breast cancer (n = 800). Total interval (TI) was determined using predefined time scales, including one referring to patient interval (PI), and several related to health care system interval (SI). Results Mean PI, SI, and TI were 4.5, 9.2, and 12.9 weeks, respectively; 20% of patients had a PI>12 weeks. Based on the multivariate regression model, longer PI was associated with perceived lack of time and personal disregard or trivialization of detected symptoms and signs. Women who were supported by family members or friends and had at least a secondary level education tended to have a shorter PI. Longer PI was correlated with a longer SI, while regular self‐examination, having been diagnosed by an oncologist, and living in a major city were associated with shorter SI. Conclusions Several factors, related to psychological, demographic, behavioral, and health system characteristics, determined both the time to seeking medical advice and treatment onset for breast cancer. These findings support review and refining of national strategies and policies to promote early detection, diagnosis, and treatment of breast cancer.