Pleomorphic lobular carcinoma in situ (PLCIS) is a more recently characterized entity that mimics high-grade ductal carcinoma in situ (DCIS). PLCIS is sometimes treated similar to high-grade DCIS, but no consensus has been reached for the most appropriate treatment. The aim of this study is to evaluate the histologic and immunohistologic profile of pure PLCIS on core needle biopsies and present follow-up clinical data. We reviewed 12 cases of pure PLCIS diagnosed on core needle biopsies of the breast along with subsequent surgical resections. Histologically, all cases showed dyscohesive cells with grade 3 nuclei, prominent nucleoli, and moderate to abundant eosinophilic cytoplasm. A panel of immunohistochemical stains to study this entity included E-cadherin, P120 catenin, estrogen receptor, progesterone receptors, HER2/neu, and Ki-67 (MIB-1). Residual PLCIS was found on excisional biopsies in 83% (10/12) cases. Invasive lobular carcinoma was found in 25% (3/12) cases. The lobular nature of all cases was confirmed by negative E-cadherin and cytoplasmic-dominant staining with P120 catenin. PLCIS was positive for estrogen receptor in 92% (11/12); progesterone receptor in 50% (6/12), and Her2/neu was positive in 25% (3/12). A moderate to high proliferation activity was observed with MIB (Ki-67) staining in 92% (11/12) cases. We conclude that PLCIS has a lobular immunostaining pattern for P120 catenin and E-cadherin indicating disruption of the E-cadherin/P120 catenin complex. This entity has aggressive parameters similar to high-grade DCIS including grade 3 nuclei, high Ki-67 (MIB-1) index, and HER2/neu positivity. PLCIS has a significant association with other high-risk lesions and invasive lobular carcinoma.