In order to describe a simple method of estimating maximum sustainable yield (MSY), we first demonstrate that the parameters of the two well-known surplus production models of Schaefer and Fox can be expressed in terms of fishing mortality that yields maximum sustainable yield (FMSY), annual yield and mean biomass. If FMSY is known, or, alternatively, is assumed to be some specified function of a known natural mortality rate, it thereby becomes possible to estimate MSY and describe the surplus production function even when the data are limited to one year of estimates for catch and mean biomass. The method is compared to other simple methods for estimating MSY and its potential application is discussed. © 1989.