Along with initial observations, our regular lidar temperature measurements over Fort Collins, CO (41 ¿N, 105 ¿W) in the rarely probed mesopause region has resulted in a unique seven-year data set between 1990 and 1997. After the seasonal variations are removed, a clear episodic warming is observable in the time series of residual temperatures. Least squares fitting the residual temperatures to an episodic impact function plus a linear trend shows maximum temperature increases occurring in 1993 with magnitudes of 9.0¿1.7 K and 12.9¿1.8 K, at 86 km and 100 km, respectively. By association, we attribute the Mount Pinatubo eruption in June, 1991, as the most probable primary cause for the observed warming, supporting a connection between tropical stratospheric aerosol and temperatures in a midlatitude mesopause region. It is hoped that our lidar observation from a single location will stimulate similar investigations at other latitudes and longitudes. ¿ 1998 American Geophysical Union