To facilitate population studies, the infestation patterns of Douglas-fir beetle, Dendroctonus pseudotsugae Hopkins, were investigated in standing and wind thrown trees in southern Idaho. Three infestation zones were recognized in most standing trees. The basal zone was infested least densely, progeny did not result from about one-fourth of the galleries, and the infestation varied more than in the upper portions. Typically, a middle zone comprised four-fifths of the infested stem, and the infestation there was densest and most successful as well as least variable. At the top of the infestation, the proportion of unsuccessful galleries again increased and fewer live progeny were present. In windthrown trees, the infestation varied circumferentially, but lengthwise stratification was not demonstrated. Both galleries and progeny were denser on the shaded underside than on the sun-exposed upper side of down trees. Although lengthwise differences were not demonstrated, the infestation was least variable mid way along the infested length, thereby favoring the underside in that vicinity for sampling of down trees.