Deadwood in forests influences fire intensity, stores carbon and nutrients, and provides wildlife habitat. We used a 54-year-old density management experiment in Larix occidentalis Nutt. forests to evaluate density dependence of woody detritus accumulation. Based on self-thinning theory, we expected woody detritus produced by the current stand to increase with stand density. Density-dependent woody detritus accumulation was apparent for fine woody debris and snags and for all woody detritus pools combined. Clear size–density relationships were apparent for coarse woody debris (CWD) and snags; mean piece size decreased with increasing stand density. Legacy CWD that originated from the preharvest old-growth stands accounted for about 45% of total woody detritus biomass. Live trees were largest in the low-density thinning treatments. Greater woody detritus biomass in the high-density and unthinned treatments originates primarily from past self-thinning, with additional inputs from density-dependent top breakage due to snow and ice and branch self-pruning. Because our results were driven by self-thinning mortality, the general trend of increasing woody detritus accumulation with increasing stand density should hold for maturing even-aged stands in other cool temperate and boreal forests.