Prediction of the impacts of volcanic mass flows (lava flows, pyroclastic density currents, debris avalanches and debris flows) is required for hazard and risk assessment, and for design of risk mitigation measures. Numerical computer-based models now exist, capable of approximating the motion of a given volume of volcanic material from its source to the deposition area. As the technology begins to mature, it is useful to compare the various models each other. A benchmark is a comparison of models aimed at simulating the same physical process upon common initial and boundary conditions and outputs, but using different physical formulations, mathematical approaches and numerical techniques. Following the approach of inter-comparison projects for volcanic ash dispersal and atmospheric models, and the 2007 Hong Kong Landslide Runout Analysis Benchmarking Exercise, we propose to set up the basis for a future general benchmarking exercise on volcanic mass flow models, primarily focusing on pyroclastic density currents and lava flows.