Human epidermal growth factor receptor 2 (HER2-neu) is an important prognostic factor associated with worsened disease-free survival and overall survival in breast cancer patients; however, the prognosis of T1a,b,N0,M0 HER2-neu positive breast cancer has not been clearly determined. Trastuzumab has become a critical component of the treatment of patients with HER2-neu positive tumors, but the effect of treatment in patients with small tumors and node-negative disease has not been evaluated in clinical trials. Current guidelines have category 3 recommendations to consider the use of adjuvant trastuzumab in women with node-negative tumors that are 0.6-1.0 cm, and state that physicians should balance the risks associated with the known trastuzumab toxicities and the uncertain benefits that may exist with such therapy in this group of patients. The available data regarding the prognosis of patients with T1a,b,N0,M0 HER2-neu positive breast cancer is very limited. The purpose of this manuscript is to review the available literature in order to evaluate whether this group of patients represents a high risk group. Retrospective studies suggest that HER2-neu status is a powerful independent prognostic factor in T1a,b node-negative breast cancer. We believe that prospective studies and randomized clinical trials are strongly needed to clearly assess the impact of HER2-neu positivity in node-negative and subcentimeter tumors, and to determine if this group of patients can benefit from adjuvant trastuzumab treatment.