Diffusion Tensor Imaging (DTI) may provide information regarding effects of 3,4-methylenedioxymethamphetamine (MDMA) use on brain structure. Twelve MDMA users and 20 healthy controls underwent whole brain DTI data acquisition. Fractional anisotropy (FA), mean diffusivity (D(av)), and longitudinal (lambda(1)) and transverse (lambda(T)) diffusivities were compared between MDMA users and controls in 6 regions of the corpus callosum. MDMA users also completed the Barratt Impulsiveness Scale (BIS), and a subset of subjects completed the Iowa Gambling Task (IGT). Results showed significantly smaller lambda(1) in the rostral body of the corpus callosum in MDMA users, with no differences between groups on lambda(T), FA, or D(av). MDMA users also had a significantly higher BIS nonplanning score and greater preference for disadvantageous choices on the IGT. There was a significant positive correlation between lambda(1) in the rostral body of the corpus callosum and advantageous choices on the IGT. Further research on the etiology of these findings is warranted.