['Gray matter (GM) pathology is an important component of the multiple sclerosis (MS) disease process. Accelerated gray matter atrophy has been observed in MS patients, but its relationship to neurological disability is not defined. This study was done to determine the relationship between whole brain, GM, and white matter (WM) atrophy and MS disability progression.', 'Patients with MS and Clinically Isolated Syndromes (CIS), and age- and gender-matched healthy controls were entered into an observational protocol. Baseline brain parenchymal fraction (BPF), GM fraction, and WM fraction, and change over 4 years were correlated with sustained disability progression over the entire study duration. Disability progression was measured using the Multiple Sclerosis Functional Composite (MSFC) and the Expanded Disability Status Scale (EDSS).', 'Seventy MS and CIS patients and 17 HCs were studied for an average of 6.6 years (range, 3.6-7.8 years). At the final visit, 7 patients were classified as CIS, 36 as relapsing-remitting MS (RRMS), and 27 as secondary progressive MS (SPMS). Baseline whole brain, GM, and WM atrophy predicted EDSS >6.0 at the last study visit. Twenty-one (33%) patients worsened using the EDSS to define disability progression; 29 (46%) worsened using MSFC to define disability progression. Patients with MSFC progression had significantly higher GM atrophy rates compared with patients who were stable on MSFC. White matter atrophy was similar in patients with and without disability progression. Atrophy rates were not different in patients with or without disability progression defined using EDSS.'] Does gray matter atrophy correlate with MS disability progression measured with MSFC but not EDSS?