Fibromatosis is a proliferation of fibroblastic and miofibroblastic cells that primarily originate from the fascia or aponeuroses of the abdominal wall. This entity has no potential metastatic risk, but can reappear locally. In rare cases it may develop in the breast, and it is extremely uncommon in the male breast. Fibromatosis of the breast presents clinical, mammographic and ultrasound signs of malignancy, and it can only be confirmed through histological analysis. We present the case of a 52-year-old man with a palpable and painless nodule in the right breast of 2 months' evolution with radiological signs of malignancy. The histological analysis determined that this was due to fibromatosis.