The increased interest in red alder (Alnus rubra Bong.) management instigated research in growth and yield and stand development of red alder in pure and mixed red alder/Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) stands. This study had the goa1s of evaluating the accuracy of the currently existing growth and yield tools for red alder and investigating the size-density relationship for pure red alder and Douglas-fir stands and mixed red alder/Douglas-fir stands. The database consisted of long-term remeasured plots in western Oregon and Washington and southwestern British Columbia. The comparison of the data with the red alder yield tables suggested lower accuracy for the Normal Yield Table for Red Alder than the Empirical Yield Table for Predominantly Alder Stands in Western Washington for prediction of both pure and mixed stand yield. Growth projections of the Stand Projection System for pure and mixed red alder/Douglas-fir stands were not accurately enough to ensure a reliable estimate of future stands conditions. The intercept and shape of the size-density trajectory and the relative density at which mortality starts (0.44) for red alder was independent of initial density. The Douglas-fir self-thinning line was above the red alder line but had a shallower slope ( -0.525 for red alder vs.-0.638 for Douglas-fir). The size-density surface for pure and mixed stands exhibited a near-linear region for stands with a high proportion of red alder and a curvilinear portion for stands with a higher proportion of Douglas-fir. Stand density, relative dominance and species proportion were found to be the major determinate of stand development. The information on the size-density relationships and stand development were incorporated into a growth model.