A new approach to defining inlet distortion factors for axial-flow compressors is presented. A summary of past analyses of inlet distortion, along with a brief review of flow-distortion definition and compressor performance, provides a background for the proposed theory. Inlet flow-distortion in terms of total-pressure fluctuations at the compressor face is vonverted to vorticity. The effects of vorticity on the internal aerodynamics of the compressor are investigated with some approximate calculations included to indicate the validity of this approach. Refinements and alternate solutions to the theory which could lead to definition of a more comprehensive and reliable definition of stall-inducing inlet distortion are included.