We describe the magnetic resonance imaging (MRI) findings of 13 cm-sized low-grade angiosarcoma of the breast that occurred in a 23-year-old woman. Magnetic resonance examination revealed an ill-defined mass with marked high-signal intensity on T2-weighted images and persistent heterogeneous enhancement. Thirty months later she developed bone metastases, incidentally found on an MRI performed to evaluate the pelvis. There were well-defined bone lesions with high-signal intensity on T2-weighted images and persistent contrast enhancement on delayed phases. The metastases were not detected on previous computed tomography and fluoro-deoxyglucose positron emission tomography scans because the lesions were subtle osteoblastic type with a low proliferative index.