Breast cancer positive for HER2 (human epidermal growth factor receptor 2) is associated with a poor prognosis for patients with both early-stage and metastatic breast cancer. Trastuzumab has been shown to be effective and is now considered the standard of care for early-stage patients with HER2-positive breast cancer. In that population, trastuzumab has been studied in six randomized clinical trials. Overall, use of this agent leads to a significant reduction in risk of disease recurrence and improvement in overall survival. Despite the strong evidence for the use of trastuzumab in managing HER2-positive early breast cancer (EBC), a number of clinical controversies remain. The authors of this paper undertook a review of the available scientific literature on adjuvant trastuzumab to produce practical considerations from Canadian oncologists. The panel focused their discussion on five key areas: (1) Management of node-negative disease with tumours 1 cm or smaller in size; (2) Management of HER2-positive EBC across the spectrum of the disease (that is, nodal and steroid hormone receptor status, tumour size); (3) Timing of trastuzumab therapy with chemotherapy for early-stage disease: concurrent or sequential; (4) Treatment duration of trastuzumab for EBC; (5) The role of non-anthracycline trastuzumab-based regimens.