The need for lighter and smaller railway traction drives and recent advances in power semiconductor technology have resulted in a new energy conversion paradigm, one without the classical heavy and bulky line frequency transformer. Several multilevel topologies have been introduced over the past years, all having in common the use of medium-frequency (MF) energy conversion to reduce the weight and volume of the magnetic components. This paper is concerned with the design of the input filter for an MF traction converter, focusing on a solution that minimizes the filter's overall mass. Two filter topologies are investigated, namely a single-pole filter (inductor) and a passively damped LCL filter. The paper first describes the requirements to be fulfilled, establishes the spectrum to consider for the design, and proposes a method to determine the initial parameters of the filter's components. The results show that an LCL-type filter achieves considerable weight savings in comparison to the single-pole solution.