Oral anticoagulants and anti-platelet therapies are used for treatment and especially prophylaxis in clinical situations where there is a risk of thromboembolism or when thromboembolic events occur. The presented case was a patient who was hospitalized due to cellulitis in the leg, and was diagnosed with heart failure, obesity and chronic obstructive pulmonary disease. She was started on prophylactic oral anticoagulants for deep vein thrombosis and pulmonary emboli and subsequently developed spontaneous breast hematoma. The usual sites of such bleeding are the skin, gastrointestinal tract, genitourinary tract, central nervous system, retroperitoneum, muscle, and the site of recent surgical procedures or trauma while breast hematomas are usually of traumatic origin. Spontaneous bleeding into the breast after anticoagulant use is rare. While using anticoagulants, it should be kept in mind that, rarely, bleeding may occur in the breast. We advise that intervention in such cases is unnecessary, no matter how large the breast hematoma is, and that new anti-coagulant drugs may be safer.