OBJECTIVES: To evaluate the patterns of metachronous metastases in patients with breast cancer. METHODS: Patients diagnosed with non-metastatic (M0) breast cancer at initial diagnosis between 2006-2008 were selected from the Eindhoven Cancer Registry, which is a population-based registry and records data on newly diagnosed cancer patients. By means of active follow-up, additional data on date of diagnosis and localization of metachronous metastases were collected directly from the patient files. Anatomical sites of metastasis were registered according to the International Classification of Diseases for Oncology (ICD-0). Proportions of metachronous metastases between tumour and treatment characteristics were compared using the Chi test. A p-value <0.05 was considered significant. RESULTS: There were 1,382 patients diagnosed with M0 breast cancer with a mean (±SD) age of 60.3 (±13.8) years. Of those, 116 patients (8%) developed metachronous metastases during a median (±SD) follow-up of 4.1 (±1.1) years. The mean (±SD) age at the time of diagnosis of metachronous metastases was 61.7 (±14.3) years. Diagnosis of metachronous metastases was confirmed by imaging in 76 patients (66%), in 39 patients (34%) by histopathology and 1 patient (1%) based on clinical symptoms. The most frequent metastatic sites affected were bone (29%) and liver (17%). Breast cancer patients who developed metachronous metastases were significantly more often diagnosed with a hormone receptor positive and a HER2-negative tumor, had a poor tumor grade, had a tumor size greater than 2.1 cm, and more often received chemotherapy at initial breast cancer diagnosis. CONCLUSIONS: Of the initially M0 breast cancer patients, 8% developed metachronous metastases, of which one-third developed bone metastasis. The risk of developing metachronous metastases varies among different characteristics at initial breast cancer diagnosis. Identifying the patterns of metachronous metastases and characteristics increasing the risk for developing metachronous metastases contributes to tailored follow-up and adequate initial M0 breast cancer treatment.