Leptomeningeal carcinomatosis (MC) represents an uncommon, but devasting manifestation of metastatic breast cancer. This is the first systematic review/pooled analysis to synthesize all available data evaluating the efficacy and safety of intrathecal (IT) administration of trastuzumab for the treatment of MC in HER2-positive breast cancer patients. This study was performed in accordance with the PRISMA guidelines. A total of 13 articles (17 patients) were eligible. The mean age of patients at IT trastuzumab administration was 48.2 years (SD 8.4, range 38-66). The mean total dose was 399.8 mg (SD 325.4, range 35-1,110 mg). IT trastuzumab alone or as part of combination therapies seemed to be safe; no serious adverse events were reported in 88.2 % of cases. In 68.8 % of cases, a significant clinical improvement was observed, while stabilization or progression of the disease was noticed in 31.2 % of cases. Cerebrospinal fluid (CSF) response was noted in 66.7 % of cases. The median overall survival was 13.5 months, whereas the median central nervous system progression-free survival (CNS-PFS) was 7.5 months. In 23.5 % of cases, IT trastuzumab was administered beyond CNS progression with a response noticed in 75 % of cases and a CNS-PFS of 9.4 months. The cumulative dose of IT trastuzumab given was 1,040 mg (SD 697.9, median 1,215, range 55-1,675). The protective effect of prior radio- or neurosurgery upon CNS-PFS was sizeable but did not reach formal statistical significance (HR 0.28, 95 % CI 0.06-1.37). Clinical improvement (HR 0.14, 95 % CI 0.02-0.91) and CSF response (HR 0.09, 95 % CI 0.01-0.89) were associated with longer CNS-PFS. IT trastuzumab administration seems to represent a safe and in some cases effective option for the treatment of HER2-positive breast cancer patients with leptomeningeal involvement. However, clinical trials are urgently needed to establish the definite role of IT trastuzumab in HER2-positive metastatic breast cancer patients with MC.