The most frequent breast inflammatory diseases are lactational and non-lactational mastitis. The diagnosis of these lesions is always difficult, as they often mimic breast cancer. The Authors report on their experience about 830 clinical cases of non-lactational mastitis, 804 were superficial abscesses and 24 were phlegmons. In 379 cases an infectious cause was found: in 249 by Streptococcus/Pseudomonas and in 30 by Staphylococcus Aureus. All patients underwent surgical treatment. Diagnosis was obtained by clinical examination, routine investigations (ultrasound, mammography and cytology) and post-operatively by histological evaluation. The nonlactational mastitis are more frequent in the postmenopausal and the menopausal period, but MDAIDS (Mammary Ducts Associated Inflammatory Diseases Sequence) are particularly interesting. MDAIDS was observed in 178 cases, these are very peculiar lesions characterized by ducts ectasia, squamous metaplasia, lymphoid infiltration and strictly correlated with heavy smoking. Sometimes, only surgical treatment clarifies the nature of these lesions. Patients with inflammatory diseases of the breast present with mastalgia and secretions, symptoms which alert patients to consult quickly a specialist. Instrumental investigations often don’t clarify the diagnosis and surgical treatment by incision and drainage or excision is definitive.