The western spruce budworm, Choristoneura occidentalis (Free.), has caused a measurable impact on a portion of the Flathead Indian Reservation during a 5-year infestation period. This survey showed that most of the grand fir and alpine fir, and 13.8 percent of the Douglas fir has been top killed in the Valley Creek area west of Arlee, Montana. The survey also disclosed that a total net growth loss of 19.6± 1.9 board feet per acre per year has occurred since 1967. Significant growth reduction at the 99 percent level occurred in Douglas-fir, grand fir, alpine fir, and western larch. Little mortality in trees 5 inches d.b.h. and greater has occurred to date. Of the trees under 5 inches d.b.h. 55.6 percent were not suitable for Christmas tree production because of insect damage.