Lobular carcinoma in situ of the breast is classified as non-invasive malignant tumor of the breast. Its diagnosis is a marker for an increased risk of developing other histological types of breast cancer. Lobular carcinoma in situ is usually asymptomatic, with no characteristic radiological features. The diagnosis is often accidental while diagnosing lesions found on screening mammography. The most important clinical issue associated with the diagnosis of lobular carcinoma in situ is the possible risk of concurrent breast cancer of another histological type. According to the current standards of managing patients with lobular carcinoma in situ of the breast, surgical biopsy of the mass is most commonly recommended. Specific principles of therapy depend on the circumstances surrounding the diagnostic process. The complete diagnosis requires histopathological study of tissue specimens from paraffin blocks. It is necessary to determine the histological subtype of the identified tumor as different subtypes present significant differences as to the course of the disease (classic lobular carcinoma in situ, pleomorphic, florid or comedo with necrosis ones). Contrary to the classic lobular carcinoma in situ, other subtypes are characterized by significantly higher risk of coexisting infiltrating breast cancer. In such cases, it is necessary to perform surgical excision of the tumor. Diagnosis of LCIS does not require surgical treatment (possible active surveillance of the patient).