SimTB is a Matlab toolbox allowing for flexible generation of fMRI datasets under a model of spatiotemporal separability and is designed to facilitate the testing of a variety of analytic methods. Users have full control over generated datasets, including the creation and manipulation of spatial sources,implementation of block- and event-related experimental designs, inclusion of tissue-specific baselines, simulated head movement, and more. Beginning MATLAB users can use the SimTB graphical user interface (GUI) to design and execute simulations while experienced users can write batch scripts to automate andcustomize this process. Please send comments and bug reports to vcalhoun@unm.edu or eallen@mrn.org.