An open study was conducted with the aim of reporting long-term clinical outcome of endovascular treatment for chronic cerebrospinal venous insufficiency (CCSVI) in patients with multiple sclerosis (MS). Twenty-nine patients with clinically definite relapsing-remitting MS underwent percutaneous transluminal angioplasty for CCSVI, outside a clinical relapse. All the patients were regularly observed over at least two years before the first endovascular treatment and for at least two years after it (mean post-procedure follow up 30.6±6.1 months). The following clinical outcome measures were used: annual relapse rate and Expanded Disability Status Scale (EDSS) score. All the patients were observed intensively (mean 6 hours) on the day of the endovascular treatment to monitor for possible complications (bleeding, shock, heart attack, death). We compared the annual relapse rate before and after treatment (in the two years before and the two years after the first endovascular treatment) and the EDSS score recorded two years before versus two years after the treatment. Overall, 44 endovascular procedures were performed in the 29 patients, without complications. Thirteen of the 29 patients (45%) underwent more than one treatment session because of venous re-stenosis: 11 and two patients underwent two and three endovascular treatments respectively. The annual relapse rate of MS was significantly lower post-procedure (0.45±0.62 vs 0.76±0.99; p=0.021), although it increased in four patients. The EDSS score two years after treatment was significantly lower compared to the EDSS score recorded at the examination two years before treatment (1.98±0.92 vs 2.27±0.93; p=0.037), although it was higher in four patients. Endovascular treatment of concurrent CCSVI seems to be safe and repeatable and may reduce annual relapse rates and cumulative disability in patients with relapsing-remitting MS. Randomized controlled studies are needed to further assess the clinical effects of endovascular treatment of CCSVI in MS.