Structural and functional abnormalities have been extensively reported in major depressive disorder, but possible changes in cortical folding have not yet been explored in this disorder. This study investigated this issue in major depressive disorder using the local gyrification index. High-resolution magnetic resonance imaging was performed in 18 patients with first-episode major depressive disorder and 18 age-matched and sex-matched healthy individuals. The local gyrification index was applied to detect brain areas with abnormal cortical folding in major depressive disorder. Compared with healthy participants, patients with major depressive disorder showed significantly decreased local gyrification index in the bilateral mid-posterior cingulate, insula, and orbital frontal cortices, the left anterior cingulate cortex, and the right temporal operculum.