Background Multiple sclerosis (MS) affects all areas of the brain resulting in both focal and diffuse damage. In Phase 3 clinical trials, fingolimod showed significant reductions in both focal lesions and rate of brain volume loss (BVL) in patients with relapsing-remitting MS. Objective To investigate if the effects of fingolimod 0.5 mg on BVL are mediated exclusively through its effects on focal damage or if fingolimod also acts independently in reducing diffuse damage. Methods This was a pooled post-hoc analysis of patients from two Phase 3 studies (FREEDOMS [N=1272] and FREEDOMS II [N=1083]), with no evidence of focal disease activity as defined by absence of gadolinium-enhancing lesions at baseline and new active lesions and clinical relapses at follow-up. The percent brain volume change (PBVC), as a measure of diffuse tissue damage, was assessed at Month (M) 12 and M24 by using the Structural Image Evaluation using Normalization of Atrophy (SIENA) method. A regression analysis was performed in the pooled intent-to-treat (ITT) population to quantify the treatment effect of fingolimod on BVL vs. placebo (PBO) in the overall population (unadjusted model), and whether this effect is sustained after adjusting for new active lesions and on-study relapses (adjusted model). Results Of 1088 patients, 638 (PBO, n=127; fingolimod, n=511) at M12 and 450 patients (PBO, n=68; fingolimod, n=382) at M24 showed no focal activity. Fingolimod significantly reduced PBVC by 65.5% over 12M (fingolimod vs. PBO: -0.16 vs. -0.45; p=0.001) and by 48.2% over 24 M (-0.42 vs. -0.81; p=0.004). An absolute difference in PBVC of -0.27% (p