Forest tent caterpillar (Malacosoma disstria Hübner) is a major defoliator of hardwoods throughout North America, including aspen (Populus tremuloides Michx.). M. disstria has been a major concern in many parts of Canada for the last two decades, but until recently in British Columbia it was considered an aesthetic concern only. However, with the increasing interest in the cultivation of hardwoods for fibre, and more recently for fuel, this insect could become a major concern in hardwood management. Records of past M. disstria outbreaks in British Columbia were summarized. The locations and intensity of six outbreaks were overlaid on biogeoclimatic units to determine which biogeoclimatic zones have experienced repeated outbreaks of M. disstria. Between 1944 and 2003, M. disstria outbreaks have become larger in extent and longer in duration. Analysis indicated that aspen stands in the Boreal White and Black Spruce (BWBS), SubBoreal Spruce (SBS) and Interior Cedar-Hemlock (ICH) biogeoclimatic zones have been most frequently attacked. In the BWBS zone, most affected areas (93.3%) were defoliated for only one year (lightly). In the SBS and ICH zones, areas attacked by M. disstria tended to be defoliated two or more consecutive years (40.2% and 56.2%, respectively), and had a greater chance of being more severely defoliated than aspen stands in the BWBS zone.