Adjuvant radiotherapy to the breast or chest wall is given to some patients with breast cancer, to reduce the risk of local recurrence. It is known to be associated with various late sequelae, including subcutaneous fibrosis, telangiectasia and pulmonary fibrosis. Delivering radiotherapy to the chest wall and nodal drainage areas presents the technical problem of matching the glancing and anterior supraclavicular fields. Overlap between these fields will result in underlying tissues receiving a larger dose than intended; similarly, a gap results in an inadequate dose. We present the case history of a patient with subcutaneous calcification occurring as a late sequela of radiotherapy to the chest wall and anterior supraclavicular field. This has not been previously reported and is thought to have arisen from a high dose region in an area of overlap between fields.