Dermatofibrosarcoma protuberans (DFSP) is a slow growing soft tissue neoplasm of dermal fibroblastic origin characterised by local invasion and a high propensity for local recurrence. We report a 31-year-old woman with subcutaneous DFSP of the breast, which is an unusual localisation. Diagnostic work-up comprised clinical examination, mammography and ultrasound. Definitive diagnosis was not possible prior to histological analysis of the lesion. Wide excision of the tumour was performed, which is the therapy of choice in DFSP. Ultrasound played an important role in histological diagnosis before definitive surgery and might be helpful in follow-up of patients with DFSP of the breast.