The m.3242A>G mitochondrial mutation is known to cause the MELAS syndrome. A group of MELAS patients was scanned using multi-parameter quantitative 7T MRI to assess brain changes related to mutation load and disease duration. Here, we focused on cortical thickness differences between control subjects and MELAS patients and within patients as a function of mutation load. MELAS patients were characterized by a reduced cortical thickness compared to control subjects in several regions. Within these regions, cortical thickness decreases with increasing mutation load for the fusiform and planum temporal gyri, which are involved in visual working memory and auditory processing, respectively.