In this talk the results of a ground-based microwave heterodyne spectrometer operated near Andenes in Northern Norway will be presented. The instrument provided an almost continuous data set of water vapor from 1995 until 2001. Under normal conditions the data is covering the altitude range from 40 to 85 km. Under certain circumstances thermospheric water vapor around 100 km altitude can be observed as well.

The measurements show a strong annual cycle with water vapor maxima in summer and minima in winter which may be modulated by dynamical events as stratospheric warmings. Within the six years of operaton we see an increase of upper stratospheric and lower mesospheric and a decrease of upper mesospheric water vapor. Twice a water vapor cloud created by space shuttle exhaust could be identified.