Diffusion-weighted magnetic resonance imaging allows researchers and clinicians to identify individual white matter fiber tracts and map their trajectories. The reliability and interpretability of fiber-tracking procedures is improved when a priori anatomical information is used as a guide. We have developed an automated method for labeling white matter fiber tracts in individual subjects based on a probabilistic atlas of fiber tract locations and orientations. The probabilistic fiber atlas contains 23 fiber tracts and was constructed by manually identifying fiber tracts in 21 healthy controls and 21 patients with temporal lobe epilepsy (TLE). The manual tract identification method required ∼40 h of manual editing by a trained image analyst using multiple regions of interest to select or exclude streamline fibers. Identification of fiber tracts with the atlas does not require human intervention, but nonetheless benefits from the a priori anatomical information that was used to manually identify the tracts included in the atlas. We applied this method to compare fractional anisotropy—thought to be a measure of white matter integrity—in individual fiber tracts between control subjects and patients with TLE. We found that the atlas-based and manual fiber selection methods produced a similar pattern of results. However, the between-group effect sizes using the atlas-derived fibers were generally as large or larger than those obtained with manually selected fiber tracks. Hum Brain Mapp, 2009. © 2008 Wiley-Liss, Inc.