PURPOSE OF REVIEW: The aim of this article is to review the latest clinical trials in neurological diseases where magnetic resonance imaging was used to assess treatment outcome. RECENT FINDINGS: The unique sensitivity of magnetic resonance imaging for detecting disorders in the brain has made it an attractive noninvasive tool for assessing treatment efficacy in several diseases. Volumetric and functional magnetic resonance imaging have proved to represent robust biomarkers for the evaluation of anti-Alzheimer treatments, and have demonstrated a significant impact of cholinesterase inhibitors. The optimization of thrombolytic therapy in acute ischemic stroke has concentrated on the quantification of the ischemic penumbra, using perfusion-weighted and diffusion-weighted imaging. Standard assessment of T2 or fluid-attenuated inversion recovery lesion load remains the method of choice to evaluate new therapeutic strategy in multiple sclerosis. Other nonconventional quantitative magnetic resonance imaging techniques such as magnetic resonance volumetry, magnetization transfer imaging, diffusion-weighted imaging, or magnetic resonance spectroscopy are increasingly used in the field. SUMMARY: Magnetic resonance imaging has become a major surrogate marker of treatment response in clinical trials of neurological disorders, offering the possibility to reduce the required sample size or to shorten the duration of the trial.