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We characterized the incidence of central nervous system (CNS) metastases after treatment with trastuzumab emtansine (T-DM1) versus capecitabine–lapatinib (XL), and treatment efficacy among patients with pre-existing CNS metastases in the phase III EMILIA study.In EMILIA, patients with human epidermal growth factor receptor 2 (HER2)-positive advanced breast cancer previously treated with trastuzumab and a taxane were randomized to T-DM1 or XL until disease progression. Patients with treated, asymptomatic CNS metastases at baseline and patients developing postbaseline CNS metastases were identified retrospectively by independent review; exploratory analyses were carried out.Among 991 randomized patients (T-DM1 = 495; XL = 496), 95 (T-DM1 = 45; XL = 50) had CNS metastases at baseline. CNS progression occurred in 9 of 450 (2.0%) and 3 of 446 (0.7%) patients without CNS metastases at baseline in the T-DM1 and XL arms, respectively, and in 10 of 45 (22.2%) and 8 of 50 (16.0%) patients with CNS metastases at baseline. Among patients with CNS metastases at baseline, a significant improvement in overall survival (OS) was observed in the T-DM1 arm compared with the XL arm [hazard ratio (HR) = 0.38; P = 0.008; median, 26.8 versus 12.9 months]. Progression-free survival by independent review was similar in the two treatment arms (HR = 1.00; P = 1.000; median, 5.9 versus 5.7 months). Multivariate analyses demonstrated similar results. Grade ≥3 adverse events were reported in 48.8% and 63.3% of patients with CNS metastases at baseline administered T-DM1 and XL, respectively; no new safety signals were observed.In this retrospective, exploratory analysis, the rate of CNS progression in patients with HER2-positive advanced breast cancer was similar for T-DM1 and for XL, and higher overall in patients with CNS metastases at baseline compared with those without CNS metastases at baseline. In patients with treated, asymptomatic CNS metastases at baseline, T-DM1 was associated with significantly improved OS compared with XL.