Objective: To determine the prevalence and associated characteristics of HER-2 overexpression in infiltrative primary breast cancer. Materials and Methods: From October through December 2003 and from May through December 2004, 274 cases of infiltrative primary breast carcinoma were studied and pathological characteristics correlation with HER-2 overexpression 3+ was determined at Edgardo Rebagliati Martins National Hospital’s Pathological Anatomy Department. Results: Three plus HER-2 overexpression was found in 64 (23,4%) cases, 2+ in 9 (3,3%) and negative (1+ or 0) in 201 (73,4%) cases. The non-specified infiltrative ductal histology type was present in 211 (77%) cases, and the infiltrative lobulillar in 27 (9,9%). We determined associated 3+ overexpression in non-specified infiltrative ductal carcinoma (p=0,0001), nipple Paget’s disease (p <0,0001), and when estrogen receptors t...