OBJECTIVES: Trastuzumab is a recently approved monoclonal antibody for the treatment of HER2 positive women with metastatic breast cancer (MBC). It shows less toxicity than cytotoxic chemotherapy. The objective of this review was to assess the safety profile of trastuzumab monotherapy in the treatment of HER2 positive women with MBC. METHODS: A comprehensive search was conducted in the Cochrane Library, EMBASE and PUBMED to identify randomised controlled trials (RCTs) and single-arm studies assessing the safety of trastuzumab, as monotherapy, in adult HER2 positive women with MBC. The searches were conducted from the database start to January 2011. Only English language studies were included. Eligibility of trials was assessed by two blinded reviewers with any discrepancy resolved by a third independent reviewer. Adverse events were the outcome of interest.  RESULTS: A total of 518 citations were retrieved of which five studies met the inclusion criteria. This constituted a total of 2229 patients. Safety data showed that gastrointestinal adverse effects (6.68%) were most frequent followed by decrease in left ventricular ejection fraction (LVEF) (6.59%), infection (3.86%), pain (3.14%), headache (2.87%), chills (2.33%), congestive heart failure (1.93%), cough (1.84%), fatigue (1.44%), dyspnoea (1.21%) and pyrexia (0.76%).  CONCLUSIONS: Results show a higher incidence of gastric and cardiac adverse events compared to other adverse events. Long term studies are required to evaluate risks that may be associated with trastuzumab.