Glatiramer acetate (GA) is effective in reducing clinical and magnetic resonance imaging (MRI) activity in relapsing-remitting multiple sclerosis (RRMS). Serial long-term MRI data are lacking for large cohorts of GA-treated patients. The European/Canadian GA study consisted of two consecutive phases, each lasting nine months. The first treatment phase was randomized, double-blind and placebo-controlled. The second was an open-label, active treatment phase with daily administration of 20 mg GA subcutaneously for all patients. For the long-term follow-up (LTFU), dual echo, pre- and postgadolinium T1-weighted brain MRI scans were obtained with the same acquisition scheme as for the original trial and a neurological assessment was performed. Lesion volumes, normalized brain volumes and percentage brain volume changes (PBVC) were measured. One hundred and forty-two (63.4%) of the 224 patients who completed the two phases of the European/Canadian study underwent the LTFU after a mean period of 5.8 years (range: 5.3-6.4); 73 were treated with GA from study initiation. MRI measures at LTFU did not significantly differ between patients originally assigned to placebo and those who were always treated with GA, but the proportion of patients who did not require walking aids at LTFU was lower in the latter group (P=0.034). PBVC between baseline and LTFU was significantly correlated with lesion load at study entry. An earlier initiation of GA treatment in patients with active RRMS might, at least partially, have a favourable impact on long-term disease evolution.