The possible relationship between Polar Mesospheric Summer Echoes (PMSE), tidal winds and vertical wind shear associated with the tidal winds is examined. PMSE were observed by the Esrange VHF MST Radar (ESRAD) 52 MHz radar at 67¿56'N, 21¿04'E during May--August 1997. Three data series in the beginning, middle and the end of the PMSE season are considered. The seasonal variation of PMSE shows a steep increase in occurrence at the end of May and fade-out in mid-August. Daily variation of echo power in the middle of the season has a minimum around 20--22 UT. Wind measurements reveal terdiurnal, semidiurnal and diurnal tides. Between 82--87 km we found a strong wind shear which tends to increase through the season, but does not show significant correlation with SNR (signal-to-noise ratio). It seems likely that PMSE appearance is conditioned by small scale dynamics and tidal effects on aerosols, and not by large scale wind shear. ¿ 1998 American Geophysical Union