In France, the off-label use of high-dose baclofen (HDB) for alcohol dependence is spreading. HDB induces frequent neuropsychiatric adverse events (AEs). Borderline personality disorder (BPD) is a major axis-two psychiatric disorder that exposes to frequent comorbid alcohol dependence and increased risky behaviors. We investigated the drinking and safety outcomes of patients with BPD treated with HDB for comorbid alcohol dependence. In a prospective cohort of 204 patients with alcohol dependence treated by HDB, 23 patients fulfilled the Diagnostic and Statistical Manual of Mental Disorders, 4th ed. criteria for BPD. We paired two control participants without a psychiatric history with each BPD patient according to age and sex. We compared the average lengths of follow-up, average doses of baclofen received, rates of heavy drinking days, rates of serious AEs, and rates of AEs resulting in baclofen withdrawal. Between BPD patients (n=23) and controls (n=46), there were no significant differences in mean age (45.3±11.2 vs. 45.2±11.2 years), sex ratio (43.5% women), mean duration of follow-up (8.0±4.0 vs. 7.7±4.2 months; P=0.77), and average daily dose of baclofen (102.2±42.7 vs. 94.6±9.7 mg/day; P=0.44). However, the mean rate of heavy drinking days (74.3±25.3 vs. 41.7±33.3%; P<10E−4), the rate of serious AEs (65.2 vs. 6.5%; P<10E−4), and the rate of treatment discontinuation after AEs (52.2 vs. 8.6%; P<10E−4) were significantly higher in BPD. The benefit/risk balance of HDB appears to be unfavorable in comorbid BPD patients compared with nonpsychiatric patients.