Increasing altitude can result in reduced diversity of exotic plants while disturbance usually benefits exotics. Species richness and cover of exotics was examined in paired 120 m2 roadside and adjacent natural vegetation plots at 10 sites along a 1000 m altitudinal gradient from montane to the alpine zone in the Snowy Mountains. Species richness and cover of exotics decreased linearly with increasing altitude in both habitats. The affect of altitude was partly off-set by disturbance with more species, and greater cover of exotics on roadside plots. There were high diversity of annual/biennial forbs particularly at low altitude, and few exotic annual/biennials above 1510 m. The decline in diversity with altitude may be due to differences in disturbance history with the highest plots having lower levels of use, but the decline in diversity is most likely due to differences in environmental conditions with increasing altitude that limit exotics, particularly annuals/biennials.