Background. The relative efficacy and safety of lacosamide as adjunctive therapy compared to other antiepileptic drugs has not been well established. Objective. To determine if lacosamide provides improved efficacy and safety, reduced length of hospital stay and improved quality of life compared with other anti-epileptic therapies for adults with partial-onset seizures. Data Sources. A systematic review of the medical literature using Medline (1946-Week 4, 2012), EMBASE (1980-Week 3, 2012), Cochrane Central Register of Controlled Trials (Issue 1 of 12, January 2012). Additional studies were identified (through to February 7, 2012) by searching bibliographies, the FDA drug approval files, clinical trial registries and major national and international neurology meeting abstracts. No restrictions on publication status or language were applied. Study Selection. Randomized controlled trials of lacosamide in adults with partial-onset seizures were included. Data Extraction. Study selection, extraction and risk of bias assessment were performed independently by two authors. Authors of studies were contacted for missing data. Data Synthesis. All pooled analyses used the random effects model. Results. Three trials (1311 patients) met inclusion criteria. Lacosamide increased the 50% responder rate compared to placebo (RR 1.68 [95% CI 1.36 to 2.08]; I(2) = 0%). Discontinuation due to adverse events was statistically significantly higher in the lacosamide arm (RR3.13 [95% CI 1.94 to 5.06]; I(2) = 0%). Individual adverse events (ataxia, dizziness, fatigue, and nausea) were also significantly higher in the lacosamide group. Limitations. All dosage arms from the included studies were pooled to make a single pair-wise comparison to placebo. Selective reporting of outcomes was found in all of the included RCTs. Conclusions. Lacosamide as adjunctive therapy in patients with partial-onset seizures increases the 50% responder rate but with significantly more adverse events compared to the placebo.