Used data collected from standardized electrofishing surveys in Washington State to develop a method to rapidly evaluate the size structure of inland fish populations. "Relative length frequency" compares the length frequency of fish from a particular lake to an average developed for a state or region. This technique is analogous to relative weight (Wr), relative condition (Kn) or relative growth, which are used to compare condition or growth of fish in a particular water body to range wide or regional standards. Relative length frequency can be used in conjunction with relative weight or relative growth to rapidly identify potential factors limiting the production of catchable-sized fish in a population.