Real-time thermal neutron radiography has been applied to the visualization of fluid flows. Since neutrons can penetrate metal casings, the technique may be useful for the visualization of fluids flowing inside metal enclosures, such as valves, engine or transmission components, etc. The technique described involves shadowgraph imaging of neutron-opaque tracer materials (either solid or fluid particles) as they convect in a stream of neutron-transparent ambient fluid. Real-time motion pictures of several simple flows have been recorded, from which velocities, regions of flow separation, rate of mixing, and other information about the flow field can be obtained. The neutron radiography facility at the Penn State Breazeale Nuclear Reactor and the studies performed to determine viable liquids useful in neutron radiography applications are described. Some examples of successful flow visualizations are also presented.