Introduction. Morphea is a rare dermatological disease with no known cause, characterized by persistent inflammation, collagen deposition, fibrosis, and atrophy, as well as a considerable reduction in quality of life. Case presentation. An 89-year-old female patient, with a history of arterial hypertension, right mastectomy, and radiation therapy for breast cancer 10 years before, presented for the appearance of two erythematous plaques in the right submammary groove and right flank. The plaques are well-defined, with irregular margins, and have dimensions of 10/5 cm, and 13/8 cm respectively, were infiltrated, with areas of skin retraction and visible capillary network, itchy and painful. They were observed six months before presentation, as a single hyperpigmented lesion that gradually evolved into its current appearance and was treated as a subcutaneous hematoma, without resolution. Laboratory tests showed a nonspecific inflammatory syndrome and an increase in antinuclear antibodies. By corroborating the clinical and paraclinical data, the diagnosis of plaque morphea was made, and the systemic treatment with Penicillin G 2mil IU/12h, 311nm UVB phototherapy was initiated, with favorable evolution. At the subsequent hospitalization, after noticing the increase in the size of the plaques, with their extension to the left hemiabdomen, it was decided to start treatment with Methotrexate 7.5 mg/week, with a favorable evolution and the disappearance of fibrous bands. Conclusions. Although radiotherapy may be the trigger factor of morphea, the time until the onset of the disease (9 years) is consistent with the data presented in the literature (9.4 years).