The Length Frequency Distribution Analysis (LFDA) package is a PC-based computer package for estimating growth parameters and mortality rates from fish length frequency distributions. Version 5.0 of LFDA includes methods for estimating the parameters of both non-seasonal and seasonal versions of the von Bertalanffy growth curve. It includes three methods for estimating growth parameters. These are Shepherd's Length Composition Analysis (SLCA) method, the projection matrix (PROJMAT) method, and a version of the Elefan method. A facility is provided that allows conversion of length frequencies to age frequencies using the estimated growth curves. In addition to methods for estimating growth parameters, the package also includes three methods for estimating the total mortality rate Z, given estimates of the von Bertalanffy parameters. A function allowing simulation of length frequency data under a variety of assumptions is also included. As with previous versions of LFDA, the package includes a comprehenive context-sensitive Help system and a detailed example analysis. The download file also includes the graphics server programme required to plot the data.