Objective: To determine the association between delayed diagnosis and advanced clinical stage breast cancer, and to explore the factors that influence this delay., Methods: Cross-sectional study of women over 18 years of age with breast cancer who attended 4 oncology centers in Medellín, Colombia, in 2017. The "Breast Cancer Delay Questionnaire" which includes sociodemographic and clinical variables as well as time intervals was used. Crude and adjusted odds ratio (OR) were estimated, using advanced clinical stage as outcome and delayed diagnosis as exposure., Results: 42 patients were included. The median time interval between the identification of the problem and the diagnostic biopsy was 104.5 days; between the identification of the problem and the first medical visit, 20 days; and between the first visit and the diagnostic biopsy, 53 days. Of all the cases, 52.1 % were diagnosed at an advanced stage. An association was found between delayed diagnosis and advanced clinical stage (OR = 2.15 95 % CI 1.21-3.79). Age above 40 was found to be a protective factor against having an advanced-stage lesion (OR = 0.35; 95 % CI: 0.14-0.83). Delayed diagnosis was associated with affiliation to the government subsidized health system (OR = 9.67; 95 % CI 2.76- 33.9) and age over 40 years (OR = 2.75; 95 % CI1.16-6.53)., Conclusions: Patient education is required in order to ensure adherence to early screening programs or timely consultation whenever a sign or symptom is identified, thus allowing diagnosis at an early stage of the disease. Moreover, prospective studies are needed in order to identify factors associated with delays in treatment after the diagnosis of breast cancer, and to assess interventions designed to reduce delays in the care of this form of cancer., Competing Interests: Investigación académica para optar por el título de Magíster en Epidemiología Clínica, (Copyright© 2020 This is an open-access article distributed under the terms of the Creative Commons Attribution License by-nc-nd/4.0.)