Transcranial direct/alternating current stimulation (tDCS/tCS) has recently seen increasing interest as a therapy for many brain disorders such as stroke, epilepsy, and depression. However, the extent of our ability to control energy delivery to target structures is not yet known. The use of large electrode arrays is expected to provide increased localization of current and voltage patterns. However, optimal excitation patterns are not trivial to design, and accurate modeling of tDCS in the whole head is critical. Here we report on an initial effort along these lines. Using a subject-specific approach, we model a human head to estimate the brain current density distribution using Finite Element Method (FEM). We pay particular attention to correct determination of skull geometry, to inclusion of conductivity anisotropy including diffusion-weighted MR modeling of white matter tracts, and to accurate modeling of electrode boundary conditions.