Mature grand firs (Abies grandis [Dougl. ex D. Don] Lindl.) were sampled in two stands, one cutover and one virgin, in the Little Salmon River drainage in west-central Idaho, to estimate stem volume losses associated with topkilling. Damage to the stands resulted from three outbreaks of western spruce budworm (Choristoneura occidentalis Freeman) in 1922-30, 1952-55, and 1969-78. Stems of the firs were dissected and examined for reductions in height and radial growth, stem deformities, and decay associated with topkills. Merchantable volume losses (to a minimum 4-inch diameter top) were calculated for each outbreak. Greatest volume loss was associated with tops killed by the 1922-30 outbreak. Loss varied widely among the trees and stands sampled. In the cutover stand, which received a sanitation cutting in the late 1960's, firs topkilled by the 1922-30 outbreak averaged losses of 9.5 ft3 (0.3 m3), amounting to 11.1 percent of merchantable stem volume. In the vigin stand, losses averaged 26.3 ft3 (0.3 m3) or 20.5 percent of stem volume. Topkill-associated decays, caused mainly by Indian paint fungus (Echinodontium tinctorium Ell. and Ev.) were responsible for most of this loss. Smaller volume losses were recorded in firs topkilled by the 1952-55 outbreak. Losses per tree averaged 3.3 ft3 (0.1 m3) or 5.4 percent in the cutover stand, and 0.5 ft3 (0.02 m3) or 0.3 percent in the virgin stand. These losses resulted mainly from height growth reductions rather than decay. No merchantable volume losses were recorded for the 1969-78 outbreak.