Objectives We performed an up-to-date meta-analysis to quantify the overall incidence and risk of severe adverse events (AEs) associated with T-DM1 in patients with breast cancer. Methods Pubmed, Embase, and oncology conference proceedings were searched for relevant studies. Data were extracted to calculate the summary incidence rate and relative risk (RR) of grade >= 3 AEs. Results A total of 5,045 patients from 7 RCTs were included in the meta-analysis. The use of T-DM1 was associated with an increased risk of severe thrombocytopenia (RR 10.66, 95% CI 3.23-35.18, P < 0.001), anemia (RR 1.68, 95% CI 1.15-2.44, P = 0.007), elevated ALT (RR 2.67, 95% CI 1.60-4.47, P < 0.001), and AST (RR 3.76, 95% CI 1.45-9.78, P = 0.007). In addition, the use of T-DM1 can increase the risk of severe hypertension (RR 1.59, 95% CI 1.03-2.45, P = 0.037) and peripheral sensory neuropathy (RR 8.13, 95% CI 1.89-35.03, P = 0.005). Conclusions Treatment with T-DM1 increases the risk of severe hematologic toxicities, hepatotoxicity, hypertension, and peripheral sensory neuropathy in patients with breast cancer, while the overall incidence of these AEs is low.