Results of a long-term study of aspect sensitivity of Polar Mesosphere Summer Echoes (PMSE) are presented using archived Poker Flat MST radar (65¿08'N; 147¿27'W) data. We have used data from the PMSE region (80- to 90-km) during the months of June and July for the years 1981--84, when three antenna beams were available, one beam pointing vertical and two beams pointing 15¿ off-vertical. Comparisons of calibrated vertical and 15¿ off-vertical monthly-average echo power profiles for each of the summer months show that VHF scattering from PMSE is strongly aspect sensitive at the lowest heights (~80 km), and exhibits a clear decrease of aspect sensitivity with increasing height. Comparison of monthly-average aspect sensitivity profiles during the four-year period shows a reasonable consistency throughout the years. The composite four-year-average aspect sensitivity profile for the months of June and July data suggests a strong tendency to isotropy at the higher mesospheric heights. ¿ 1998 American Geophysical Union