To evaluate the safety and efficacy of long-term glatiramer acetate (GA) therapy, 46 patients with relapsing-remitting multiple sclerosis (RRMS) were treated for up to 22 years in an ongoing, open-label study. Kurtzke expanded disability status scale (EDSS) was measured every six months, relapses were reported at occurrence and patients self-reported adverse events (AEs). At GA initiation, disease durations ranged from 0-20 years (median 6.0 years) and at data cut-off (October 2004), GA therapy duration ranged from 1-22 years (median 12.0 years). Mean EDSS score increased 0.9 +/- 1.9 from the pretreatment score (3.0 +/- 1.8; P = 0.076). Only 10/28 (36%) patients with baseline EDSS <4.0 had a last observed value >or= 4.0 and 8/34 (24%) with entry EDSS < 6.0 reached EDSS >or= 6.0. A majority (57%) maintained improved or unchanged EDSS scores. Annualized relapse rate decreased to 0.1 +/- 0.2 from 2.9 +/- 1.4 prestudy (P < 0.0001). Of the 18 remaining patients in October 2004 (average disease duration 23 years), 17% with baseline EDSS scores < 4.0 reached EDSS >or= 4.0 and 28% with baseline scores < 6.0 reached EDSS >or= 6.0. Adverse events were similar to those reported in short-term clinical trials. This study shows a low rate of relapses and EDSS progression in RRMS patients on GA for up to 22 years.