Carcinomatous mastitis is a severe form of breast cancer and its diagnosis is essentially clinical and histological. The first examination to perform is still mammography, not only to provide evidence supporting this diagnosis but also to search for a primary intramammary lesion and assess local/regional spread. It is essential to study the contralateral breast for bilaterality. Ultrasound also provides evidence supporting inflammation, but appears to be better for detecting masses and analysing lymph node areas. The role of MRI is debatable, both from a diagnostic point of view and for monitoring during treatment, and should be reserved for selected cases. An optimal, initial radiological assessment will enable the patient to be monitored during neoadjuvant chemotherapy.