Breast cancer is the most common malignant neoplasm in the world among women. As a result of the dissemination of population screening programmes, about half of non-metastatic breast cancers are now diagnosed at stage I. 10–15% of T1abN0 tumours over-express human epidermal growth factor (HER-2). These tumours have a globally excellent prognosis, however, treatment with chemotherapy and/or targeted therapy may further improve outcomes in selected cases. In this article, we will review studies with information on prognosis and benefit of adjuvant therapy for T1abN0 HER-2 breast cancer.