AbstractTracking progression in neurodegenerative diseases is hampered by the limitations of the clinical rating scales, which are seldom linear, suffer from floor and ceiling effects, lack the ability to distinguish symptomatic change from disease modification, and are limited by imperfect intra‐ and inter‐rater reliability. The promise of an era of neuroprotective therapies renders urgent the search for reliable measures of progression. Biomarkers have the potential to enhance several aspects of both therapeutic trials and clinical practice. MRI‐based measures of cerebral volume can provide a surrogate for neuronal loss and several techniques have been applied to elucidate disease processes, aid diagnosis, and enable monitoring of progression in a variety of Parkinsonian disorders, including Parkinson's disease, dementia with Lewy bodies, multiple system atrophy, progressive supranuclear palsy and Huntington's disease. We review the approaches to, and findings revealed by, serial volumetric MRI in these disorders. © 2009 Movement Disorder Society