The Density Management Diagram (Drew and Flewelling, 1979) is the graphic representation of a stand growth model, a device for silvicultural planning allowing the user to set a production target and then select combinations of initial spacings and thinnings to achieve the objective. The effectiveness of the diagram as a planning tool depends more on the accuracy of the underlying model than on ease of use, since inaccurate or biased predictions may have serious consequences. This paper evaluates the yield predictions made with the Density Management Diagram for coastal Douglas-fir.